Genetics and Inheritance

Define the following. Give an example in corn from the lab of each:

Allele

Genotype

Phenotype

Homozygous

Heterozygous

Dominant

Recessive

Define the following in your notebooks:

1. Genetics

2. Inheritance

3. chromosome

4. DNA

5. RNA

6. Protein

7. homologous chromosome

8. autosome

9. sex chromosome

10. Fertilization

11.Gene

12.Trait

13.Allele

14. Segregation

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15. Gametes

16. Dominant

17. Recessive

18. Homozygous

19. Heterozygous

20. Genotype

21. Phenotype

22. Independent assortment

23. Punnett square

24. Incomplete dominance

25. Codominance

26. Multiple allele traits

27. Sex-linked traits

28. Crossing Over

29. Sexual reproduction

30. Asexual reproduction

Chromosome –compact structures of DNA

• An average human DNA strand can stretch 1 meter.
• DNA folds 7000 times to form a chromosome
• DNA wraps around histone proteins (wrapped DNA is inactive, so histones can control gene expression)

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I80 runs 2916 miles from San Francisco, CA

to Teaneck, NJ

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Compacted 7000 fold--0.42 miles

<1/10th Bay Bridge

What is 7000 fold compaction?

I. Anatomy of a Chromosome

• Chromosome – single DNA coiled into a dense structure for cell division
• Replicated chromosome – 2 copies of a DNA held together by a centromere
• Sister chromatid – each identical copy of DNA in a replicated chromosome

A. Human chromosomes

• Normal human cells have 46 chromosomes, or ____ pairs of chromosomes.
• Therefore, humans have ____ DNA molecules in each cell.
• When cell’s divide they copy their DNA, therefore have ______ total DNA molecules and ______ replicated chromosomes.

In humans:

• ___ chromosomes per cell
• ___ chromosomes per reproducing cell

B. Genome

• Genome – all genetic material of an organism.
• Each cell in a human contains the entire human genome or all ____ chromosomes.

C. Chromosome types

• Autosomes
• non-sex chromosomes

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• Sex chromosomes
• determine the sex of an organism

How many chromosomes are in each human somatic cell?

1. 1
2. 2
3. 22
4. 23
5. 44
6. 46
7. 48

How many autosomes are in a human cell?

1. 2
2. 23
3. 44
4. 46

How many sex chromosomes are in a human cell?

1. 2
2. 23
3. 44
4. 46

Gorillas have 48 chromosomes in each cell. How many sex chromosomes do they have?

1. 2
2. 23
3. 24
4. 44
5. 46
6. 48

Y Chromosome

Chromosome number

• Sexual reproducing organisms have 2 copies of each chromosome in their cells.

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• They receive 1 copy of each chromosome from each parent.

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• The pairs of chromosomes are called homologous chromosomes.

D. Homologous chromosomes

• Homologous chromosomes (homologues) are the same size and shape and carry the same genes for the same traits.
• Homologous chromosomes are the pairs of chromosomes; 1 from each parent

How many chromosomes is in a sperm or egg cell?

1. 2
2. 23
3. 44
4. 46

• Cells with 2 sets of chromosomes are diploid (2n).

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• Cells with 1 set of each chromosome are haploid (1n).

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• Sperm and egg are the only cells in your body that are haploid.

Questions for review

1. Humans have _________ number of chromosomes in their body cells
2. Humans have _________ number of chromosomes in their sex cells
3. How many autosomes are in a body cell?
4. How many sex chromosomes are in a body cell?
5. How many autosomes are in a sex cell?
6. How many sex chromosomes are in a sex cell?
7. How many chromosomes are in the human genome?

Human Chromosomes

E. Karyotype

Karyotype – a picture of an individual’s chromosomes arranged from largest to smallest

Amniocentesis

Trisomy 21; Down Syndrome

Can survive to age 50

Mental retardation

Normal male, XY

Trisomy 21; Down Syndrome

Can survive to age 50

Mental retardation

Trisomy 13; Patau Syndrome Trisomy 18; Edwards Syndrome

Most fetuses spontaneously abort

Those that make it die in first year

Turner syndrome, XO

Female

Short, wide-chested

Underdeveloped breasts

Rudimentary ovaries

Sterile

Normal intelligence

Klinefelter syndrome, XXY

Male

Phenotype of syndrome

not apparent until puberty

Breast development

Low fertility

Subnormal intelligence

XYY Syndrome

XYY Individuals

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~5% criminals with violent and antisocial behavior are XYY,

but only 0.1% of males in population XYY

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Does this syndrome cause violent behavior?

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Should this syndrome be used as a defense in criminal trials?

XXX Females are normal

XXXX and XXXXX females also exist

SRY is both necessary and sufficient for male development

The mouse on the left is XY and the mouse on the right is XX with the sry gene inserted into its X crhomosome. Both are functioning males!!!

SRY is a transcription factor that binds DNA and regulates the expression of other genes.

Male-specific behaviors are controlled by SRY!

Tasting PTC

phenylthiocarbamide

Dominant?

Recessive?

Genotype?

Phenotype?

Allele?

If PTC tasting is dominant and Chuck is a taster for PTC, what are his possible genotypes?

If Chuck got a recessive allele from his father, what allele did he get from his mother?

Gregor Mendel

• Founder of modern genetics (1850s)
• Austrian monk who experimented with pea plants
• Discovered that inherited traits were passed down in units, later called _________________

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Mendel’s Pea Plants (28,000!)

• Used many different traits for his experiments
• Used different alleles for each trait
• ______________ – alternative forms of a gene or trait

Review Questions?

1. What is the difference between a trait and allele?
2. What is the trait and the alleles in the picture to the right?
3. Name a human trait and the alleles of that trait.

Mendel's work showed:

1. Each parent gives one allele of each trait to offspring.
2. Each pair of alleles separate from each other when forming sex cells.
3. Males and females contribute equally to the traits in their offspring.
4. Two different traits are passed down independently from each other.

Which is the trait which is the allele

• Shape of red blood cells(t/a)
• Sickle celled anemia(t/a)
• Short(t/a)
• Height(t/a)
• 5 fingers(t/a)
• Number of digits(t/a)
• Hair color(t/a)
• Blonde(t/a)
• Color of skin(t/a)
• Albino(t/a)
• Forked tongue(t/a)
• Shape of tongue(t/a)
• Gait(t/a)
• Trotting gait(t/a(
• Wrinkled seeds(t/a)
• Seed shape(t/a)
• Shape of chloride ion channels(t/a)
• Normal(t/a)
• Cystic fibrosis(t/a)

Mendel’s results produced 3 principles of inheritance

1. Dominance
2. Segregation
3. Independent Assortment

1. Complete Dominance

For a heterozygous trait where an individual has inherited two different alleles for a trait:

The pattern of inheritance is complete dominance if one allele completely masks the other allele.

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When Gregor Mendel bred pure tall plants with pure dwarf plants all offspring were tall.

What was the dominant allele?

When Gregor Mendel bred pure tall plants with pure dwarf plants all offspring were tall.

What allele was being masked in the offspring?

When Gregor Mendel bred pure tall plants with pure dwarf plants all offspring were tall.

What was the genotype of the tall offspring?

• __________________- When the two alleles are the same.

BB or bb, YY or yy

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• ________________- When the two alleles are different, in such cases the dominant allele is expressed.

Bb, Yy, Rr, Ss…

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• Capital letters = ______________alleles
• Lower case letters = __________ alleles

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• T T = ___________
• T t = ___________

(dominant alleles mask

recessive alleles)

• t t = ____________

How to make a Punnett Square:

1.Write the parents genotypes and phenotypes:

Tt x Tt

(Tall) (Tall)

2. Write the possible parent alleles on the Punnett Square:

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3. Fill in the possible offspring in the Punnett Square boxes:

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4. Calculate the probabilities of the phenotypes:

Tall = ________ Short = __________

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T t

T t

T

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t

T

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t

Examples of Punnett Squares

More Examples of Punnett Squares

Punnett Squares

Complete the following punnett squares.

Female Dark pigment (Dd) rabbit bred with a male light pigment (dd) rabbit.

Which parent was homozygous?

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Punnett Squares

Complete the following punnett squares.

Female Dark pigment (Dd) rabbit bred with a male light pigment (dd) rabbit.

What was the phenotype of the female rabbit?

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Punnett Squares

Complete the following punnett squares.

Female Dark pigment (Dd) rabbit bred with a male light pigment (dd) rabbit.

What was the genotype of the female rabbit?

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Female Dark pigment (Dd) rabbit bred with a male light pigment (dd) rabbit.

What was the probability of this pair having a dark pigmented offspring?

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In humans a type of albinism is due to a dominant allele, normal pigment is the result of a recessive allele. If the mother has normal pigment and the father is heterozygous...

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What is the mother’s genotype?

In humans a type of albinism is due to a dominant allele, normal pigment is the result of a recessive allele. If the mother has normal pigment and the father is heterozygous...

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What is the father’s genotype?

In humans a type of albinism is due to a dominant allele, normal pigment is the result of a recessive allele. If the mother has normal pigment and the father is heterozygous...

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What is the mother’s phenotype?

In humans a type of albinism is due to a dominant allele, normal pigment is the result of a recessive allele. If the mother has normal pigment and the father is heterozygous...

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What is the father’s phenotype?

In humans a type of albinism is due to a dominant allele, normal pigment is the result of a recessive allele. If the mother has normal pigment and the father is heterozygous...

Make a Punnett Square

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In humans a type of albinism is due to a dominant allele, normal pigment is the result of a recessive allele. If the mother has normal pigment and the father is heterozygous...

What percentage of offspring will have albinism? (Answer between 0-100)

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Non Mendelian Genetics

You will be assigned one pattern of inheritance.

1. Research pattern of inheritance.
2. Explain:
1. Pattern of inheritance
2. Expected outcome from heterozygous x heterozygous parents.
3. Expected outcome from heterozygous x homozygous parents.
4. Compare this pattern with complete dominance.
3. Group explanations:
• Half of your group will go to another group and take notes on the pattern of inheritance.
• Other half of group will go to another group.
4. Quiz on pattern of inheritance.

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Blood typing experiment

The ABO blood type gene is controlled by 3 alleles: I^A, I^B, and i. The +/- blood type gene is controlled by 2 alleles: Positive type is dominant (D) and negative type is recessive (d).

Test the blood samples and list the phenotypes and all possible genotypes of each patient.

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In peas Yellow (Y) is dominant to green (y).�Round (R) is dominant to wrinkled (r).�

Parents were dihybrid (RrYy).

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What are the possible gametes for each parent?�Complete a Punnet square.

2. Principle of Segregation

• The alleles are separated (segregated) when forming gametes
• Offspring receive 1 of the 2 alleles of a gene

Organisms don’t just inherit one trait or gene

• Mendel considered how pea plants inherit 2 different traits
• Seed color: Yellow (Y) and Green (y)
• Seed shape: Round (R) and Wrinkled (r)
• Discovered that traits are inherited _________________from one another

3. Principle of Independent Assortment

• During gamete formation, alleles in one trait separate into gametes independently of the alleles of another trait.
• SMA from the SMN gene is recessive (a).
• Breast cancer from the BRCA1 gene is recessive (b).

Parent: Normal,Normal Normal, Normal

Aa Bb x Aa Bb

↓ ↓

cont.

• Mother: RrYy
• Father: RrYy

1)How many traits? 2

2)How many different alleles?4

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3)Make the Punnett Square…

(on next slide)

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Genetics of Corn Lab

1. Count 2 rows recording the following phenotype combinations:
2. Calculate the observed percentages of each phenotype combination:
3. What are the dominant and recessive alleles?
4. What are the genotypes and phenotypes of the parents?

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Quiz: In corn purple is dominant to yellow and smooth is dominant to wrinkled. Additionally, tall is dominant to short.

1. A parent is Pp Ss TT, what is the chance of producing this gamete: psT?
2. What is the chance of parents that are both dihybrid (Pp Ss) having an offspring that is yellow and wrinkled?
3. If one parent is PpSs and the other parent is ppss, what phenotype would be unlikely if the genes are linked. Assume that the dihybrid parent’s dominant alleles are on the same chromosome.

1. Cystic fibrosis, normal (ffPp) x normal, PKU (Ffpp)
2. Albino, Blind (AaBb) x Normal, Normal (aabb)
3. Migraine, Diabetes (MMii) x Normal, Normal (mmIi)
4. Normal, normal, normal (AaFSs) x normal, normal, normal (AaFSs)

aa – sickle cell anemia

ff – cystic fibrosis

ss – spinal muscular atrophy (SMA)

1. Mother is Albino, Blind (AaBb) x Father Normal, Normal (aabb)

1. Albinism in this case is ____________
2. Blindness in this case is ___________
3. What are the alleles that the mother can pass down?
4. What are the alleles that the father can pass down?
5. Punnett Square.
6. What is the probability of having an albino and blind offspring?
7. What is the probability of having a blind offspring?

• Cystic fibrosis is recessive condition (ff), PKU is a recessive condition (pp). Cystic fibrosis, normal (ffPp) x normal, PKU (Ffpp)
• Albino can be a dominant condition, blindness can be a dominant condition (Albino, Blind (AaBb) x Normal, Normal (aabb)

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Determine the phenotype probabilities of the offspring for question 1 and 2.

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• Migraine, Diabetes (MMii) x Normal, Normal (mmIi)
• Normal, normal, normal (AaFfMm) x normal, normal, normal (AaFfMm)

aa – sickle cell anemia

ff – cystic fibrosis

mm – spinal muscular atrophy (SMA)

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Determine the phenotype probabilities of the offspring for question 1 and 2.

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• Cystic fibrosis is recessive condition (ff), PKU is a recessive condition (pp). Cystic fibrosis, normal (ffPp) x normal, PKU (Ffpp)
• Albino can be a dominant condition, blindness can be a dominant condition (Albino, Blind (AaBb) x Normal, Normal (aabb)
• Migraine, Diabetes (MMii) x Normal, Normal (mmIi)
• Normal, normal, normal (AaFfMm) x normal, normal, normal (AaFfMm)

aa – sickle cell anemia

ff – cystic fibrosis

Mm – spinal muscular atrophy (SMA)

Manifestations of cystic fibrosis

Homework

1. Cystic fibrosis (CF) is a recessive human genetic disease. What are the phenotypes of individuals FF, Ff, or ff for the CF gene?
2. For the CF gene what is the dominant phenotype? What is the recessive phenotype?
3. Can two individuals with CF ever have a child without CF? Justify your answer including a Punnett square.
4. Can two individuals without CF ever have a child with CF? Justify your answer including a Punnett square.
5. Based on your answers to 3 and 4, describe a pattern of inheritance for parents who both have recessive phenotypes in contrast to parents that both have dominant phenotypes.

1. Cystic fibrosis, normal (ffPp) x normal, PKU (Ffpp)
2. Albino, Blind (AaBb) x Normal, Normal (aabb)
3. Migraine, Diabetes (MMii) x Normal, Normal (mmIi)
4. Normal, normal, normal (AaFfSs) x normal, normal, normal (AaFfSs)

aa – sickle cell anemia

ff – cystic fibrosis

ss – spinal muscular atrophy (SMA)

Pea Plants

Yellow = dominant (Y), green = recessive

Round = dominant (R), wrinkled = recessive

Yyrr x yyRr

1. Parents phenotypes?
2. Possible gamete alleles?
3. Punnett Square
4. Probability of offspring phenotypes?

Other Patterns of Inheritance

Other Patterns of Inheritance

Incomplete dominance – where the heterozygous offspring look in between the 2 alleles

• Red flowers (RR) and white flowers (rr), make _________________ flowers (Rr)

Codominance – where both alleles are expressed, and do not blend in a heterozygous offspring

• Red horse coat (RR) and White horse coat (R’R’), make _________________ horse coats (RR’)

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1. What is the pattern of inheritance?
2. Which color is heterozygous?

3. What is this pattern of inheritance?

4. Brown is (CC) and chinchilla is (c^chc^ch). Predict the phenotype of a Cc^ch rabbit.

4. A roan horse has red and white hair caused by mating a red horse with a white horse. What is the pattern of inheritance?

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What is the pattern of inheritance?

What

PTC results

Genetic tests were performed on both parents that were heterozygous PTC tasters

Male tasters = 380 , Female tasters 370

Male non-tasters = 123, Female non-tasters = 127

1. What are the genotype and phenotype of the parents?
2. What is the dominant allele?
3. What is the pattern of inheritance?

Extending Mendelian Genetics for Two or More Genes

Polygenic inheritance: Some traits may be determined by two or more genes

Polygenic Inheritance

• Skin color in humans is an example of polygenic inheritance

Figure 14.13

Eggs

Sperm

Phenotypes:

Number of�dark-skin alleles:

0

1

2

3

4

5

6

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₈

¹/₆₄

⁶/₆₄

¹⁵/₆₄

²⁰/₆₄

¹⁵/₆₄

⁶/₆₄

¹/₆₄

AaBbCc

AaBbCc

Figure 14.12

Sperm

Eggs

9

: 3

: 4

¹/₄

¹/₄

¹/₄

¹/₄

¹/₄

¹/₄

¹/₄

¹/₄

BbEe

BbEe

BE

BE

bE

bE

Be

Be

be

be

BBEE

BbEE

BBEe

BbEe

BbEE

bbEE

BbEe

bbEe

BBEe

BbEe

BBee

Bbee

BbEe

bbEe

Bbee

bbee

What is the genotype of X?

What is the phenotype of X?

What is the phenotype of Y?

What is the genotype of Y?

What is the phenotype of Z?

Explain why a black and chocolate labrador can have the same genotype EE or Ee.

Explain why a black and yellow labrador can have the same genotype BB or Bb.

What is the phenotype of dog 6?

How can a yellow dog (3) and a chocolate dog (4) have a black offspring (6)?

What is the pattern of inheritance for the coat color of labradors?

4 o'clock flowers have three flower colors: red, white and the heterozygote is pink. If two pink flowers produced offspring, what is the probability of the offspring being pink flowers?

What is the pattern of inheritance for the color of 4 o’ clock flowers?

Multiple Alleles - Most genes have more than two alleles for a single gene

For example, ABO blood group in humans on red blood cells:

• Alleles: I^A (dominant allele) = Type A� I^B (dominant allele) = Type B

i (recessive allele) =Type O

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Figure 14.11

Carbohydrate

Allele

(a) The three alleles for the ABO blood groups and their� carbohydrates

(b) Blood group genotypes and phenotypes

Genotype

Red blood cell�appearance

Phenotype�(blood group)

A

A

B

B

AB

none

O

I^A

I^B

i

ii

I^AI^B

I^AI^A or I^Ai

I^BI^B or I^Bi

A mother is heterozygous for type A blood and the father is heterozygous for B blood.

What are all the possible blood types for their children?

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5. The Environmental Impact on Phenotype

• Another departure from Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype
• The phenotypic range of a genotype can be influenced by the environment
• For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil pH

Figure 14.14

X-linked traits and Y

-linked traits

Genes located on the X and Y chromosomes.

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Human X and Y chromosome. Which is which?

X-linked traits

For example, colorblindness is a recessive allele (c) only found on the X chromosome.

What are the phenotype probabilities of a cross between an XX female carrier of colorblindness and a normal sighted XY male?

If a father is colorblind (X^cY) will he pass this on to his sons?

X-linked traits (on X chromosome only)

• Traits only found on the X chromosome
• Not autosomal
• Color Blindness, Hemophilia, Duchenne muscular dystrophy
• Can never be passed from father to son
• Why?

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• Human eye can detect light in the 400-700 nanometer (nm) range

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Practice Problems

1. Possible genotypes for colorblind males:
2. Possible genotypes for males with normal vision:
3. Possible genotypes for colorblind females:
4. Possible genotypes for females with normal vision:
5. Why can’t males be heterozygous for the colorblindness, Duchenne muscular dystrophy, or hemophilia traits?

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X^HX^h x X^HY�What is the typical female?

1. Has hemophilia
2. Has hemophilia and is not a carrier
3. Does not have hemophilia
4. Does not have hemophilia and is a carrier

X^HX^h x X^HY�What is the typical male?

1. Has hemophilia
2. Has hemophilia and is not a carrier
3. Does not have hemophilia
4. Does not have hemophilia and is not a carrier

Draw a Punnett Square� X^HX^h x X^HY

• What are the possible offspring?

X^HX^H x X^hY�What is the male?

1. Has hemophilia
2. Has hemophilia and is not a carrier
3. Does not have hemophilia
4. Does not have hemophilia and is not a carrier

� X^HX^h x X^HY

What is the phenotype of the parents?

Hemophilia is a recessive X-linked condition.

� X^HX^h x X^HY

What is the chance of having a typical male with hemophilia?

� X^HX^h x X^HY

What is the chance of having a typical female with hemophilia?

Meiosis: Sex-cell Formation

• What is the main

advantage of sexual reproduction?

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• What does Mitosis do?

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_________________  - reproductive cells (ovum and sperm) that carry only 1 of each homologous chromosome.

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Twins

• Identical twins (monozygotic)
• exact same genetically (same egg and sperm)
• Fraternal twins (dizygotic)
• different genetically (different egg and sperm)

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Identical Twins & Fraternal Twins

Studying Human Inheritance

Pedigree- a family record that shows how a trait is inherited over several generations.

Birth Sex Male

Birth Sex Female

Pedigree of the Hapsburg Lip and Jaw

Affected traits can be dominant or recessive

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1. How many generations are shown?
2. Is the affected phenotype dominant (D) or recessive (r)
3. What are the genotypes of individuals 1, 3, and 9.
4. What sex chromosomes does 16 have?

Birth Sex Male

Birth Sex Female

The following is the pedigree of a trait controlled by __________ genotype.

*Determine the genotypes for as many of the offspring as possible.

Determine the genotypes

What is this pedigree?

1. Dominant
2. Recessive

Identify the blood type

1. A+
2. A-
3. B+
4. B-

1. What are the phenotypes of I-1, II-1, and III-1?
2. What are the genotypes of I-1, II-1, and III-1?
3. From whom did individual III-2 inherit his DMD trait?

Pedigree of Duchenne Muscular Dystrophy

X^c

Pedigree of Duchenne Muscular Dystrophy

What is the phenotype of someone with the X^dX^d genotype?

Pedigree of Duchenne Muscular Dystrophy

What is the phenotype of someone with the X^dY genotype?

Pedigree of Duchenne Muscular Dystrophy

What is the phenotype of someone with the X^DX^d genotype?

What usually determines the sex of human males?

The sex of most turtles, alligators, and crocodiles is determined after fertilization. The temperature of the developing eggs is what decides whether the offspring will be male or female. This is called temperature-dependent sex determination, or TSD.

Research shows that if a turtle's eggs incubate below 81.86 Fahrenheit, the turtle hatchlings will be male. If the eggs incubate above 87.8° Fahrenheit, however, the hatchlings will be female. Temperatures that fluctuate between the two extremes will produce a mix of male and female baby turtles.

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What is the sex of a turtle that incubated at temperatures between 75-80 degrees?

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A Pedigree of Hemophilia in the Royal Families of Europe

• Meiosis separates one copy of each homologous chromosome into each new "gamete".

The purpose of meiosis is to create genetically unique sex cells by:

• Rearranges the parents’ chromosomes.

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• Reduces the amount of chromosomes in half (Humans: 46 → 23)

Stages of Meiosis

Meiosis I:

Prophase I

Metaphase I

Anaphase I

Telophase I

Meiosis II:

Prophase II

Metaphase II

Anaphase II

Telophase II

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A. Meiosis I:

Before Meiosis starts interphase takes place

• DNA replicates (Humans 46 → 92 chromosomes)

1. Prophase I:

Most important stage in meiosis

• Homologous chromosomes pair together.
• Homologous chromosomes may exchange sections of chromatids in a process called _________________ _________________

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Crossing Over

2. Metaphase I

• Homologous chromosomes line up along the equator
• Chromosomes randomly line up along the equator (for example, 13 of mother’s chromosomes may be on the north side, 10 of mother’s would be on the south side)

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3. Anaphase I

• Homologous pairs split apart
• This is how you only pass on ½ your genes
• Some of the mother’s chromosomes move to one pole, father’s to the other
• _________________ chromosomes do not split. _________________ holds the _________________chromosomes together throughout Meiosis I.

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4. Telophase I

• Nucleus forms around replicated chromosomes.

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Telophase

After telophase I, DNA does NOT copy itself!

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Telophase

Meiosis

B. Meiosis II is identical to mitosis except for the number of chromosomes is exactly ½.

5. Prophase II

6. Metaphase II

7. Anaphase II

8. Telophase II

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• http://www.biologyinmotion.com/cell_division/
• http://www.pbs.org/wgbh/nova/miracle/divide.html#

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What stage is this?

1. Enter answer text...

Variation by sexual Reproduction

1. _________________ _____________: mixes the mother’s and father’s chromosomes during prophase I to make unique gametes.
2. Homologous pairs separate during anaphase I. New individuals inherit only ______________of their parents chromosomes.
3. _________________ : Fusion of two unique cells into one new individual.

Comparing Meiosis and Mitosis

1. Chromosome behavior

a. _________________ : Homologous chromosomes independent

b. _________________ : Homologous chromosomes pair until anaphase I

2. Chromosome number- reduced in meiosis

a. _________________ identical daughter cells

b. _________________ daughter cells haploid

3. Genetic identity of offspring:

a. _________________ : identical daughter cells

b. _________________ : daughter cells have new assortment of parental chromosomes

c. _________________ : chromatids not identical, crossing over

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Advantage of Sexual Reproduction

Introduces genetic variation through:

• Crossing over in prophase I
• Independent assortment of chromosomes in meiosis I
• Fertilization of unique gametes

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Allows adaptations to variable environments.

Advantages of Asexual Reproduction

Genetically identical, no variation

• Simple – no meiosis, fertilization, only one parent needed

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Clones – If well adapted to environment all offspring will be equally well adapted

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What is the purpose of a gene?

The purpose of a gene is to provide the code for the instructions to produce proteins.

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What are genes?

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Sequence of DNA that codes for a protein and thus determines a trait.

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What does allele mean?

A different form of a gene.

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Homozygous

Homozygous has identical pairs of genes for any given pair of hereditary characteristics.

A

A

A

A

AA

AA

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AA

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AA

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These parents are homozygous with a dominant allele for large ears. The outcome of large ears is 100%

heterozygous

Have dissimilar pairs of any hereditary.

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