GeneticsQuick Review of Grade 11

Sex Linked TraitsSex Influenced Traits

Polygenic TraitsEpistatic Genes

How many chromosomes do humans have?

• 46…or 23 homologous pairs

• 23 from your mother and 23 from your father

•Which chromosomes determine if you’re a girl or boy?

• Pairs1 through 22 = autosomal chromosomes

Two Types of Cells1. Somatic Cells – All body cells,

diploid (2n)2. Sex Cells – Gametes, haploid (n)

Two Types of Chromosomes1. Autosomal – All body cells2. Sex Chromosomes – X and Y

The Sex chromosomes

If you get a Xyou’re a girl

Its all up toDad….

The Sex chromosomes

But... If you get a Y you’re a boy

Punnett Squares

X XXY

XX XXXY XY

The set of genes that an organism

possesses

Expressed trait (physical appearance)

When two alleles are identical

Ex. DDWhen the two alleles are different

Ex. Dd

Different forms of the same

gene

Allele which controls the characteristic whenever it is present.

Allele whose characteristics only show up when it is present on both chromosomes

BB or Bb

bb

GeneticsQuick Review of Grade 11

Sex Linked TraitsSex Influenced Traits

Polygenic TraitsEpistatic Genes

Sex Linked Traits

• Sex-linked traits are traits that are controlled by genes on the sex chromosomes

• Examples: –Colour Blindness–Hemophilia

3 Different Forms of Sex Linked Inheritance

1. X-linked recessive inheritance2. X-linked dominant inheritance3. Y-linked inheritance

Sex Linked Inheritance Notation

• X-linked recessive alleles are represented by a X with a superscript of either:

+ (dominant) or

– (recessive)

Genotypes of Sex Linked Inheritance

• What are the possible genotypes of a sex linked inheritance for a female?

X+X+ X+X - X -X -

• What are the possible genotypes for sex linked inheritance for a male?

X+Y - X - Y

1. X-linked Recessive Inheritance

X-linked recessive traits are traits resulting from a recessive allele on the X chromosome

Why do X-linked recessive traits show up more often in men than women?

Are YOU Colorblind?

Normal Color Vision:A: 29, B: 45, C: --, D: 26

Red-Green Color-Blind:A: 70, B: --, C: 5, D: -- 3.

Red Color-blind:A: 70, B: --, C: 5, D: 6 4.

Green Color-Blind:A: 70, B: --, C: 5, D: 2

X-linked Recessive Inheritance

• Example #1: Colorblindness

• The allele that controls colorblindness is found on the X chromosome and is recessive

• What genotype must a female have to be diagnosed as colorblind?

X -X-

Possible Colorblindness Phenotypes

X+X+

Female with Normal Vision X+X –

Female with Normal Vision (Carrier)X -X –

Colour Blind FemaleX+Y –

Male with Normal VisionX – Y

Colour Blind Male

Let’s try a cross: X+X– • X+Y

• Phenotypes– Females:– Males:

Let’s try a cross: X+X– • X-Y

• Phenotypes– Females:– Males:

Let’s try a cross: X+X+ • X-Y

• Phenotypes– Females:– Males:

Let’s try a cross: X-X- • X+Y

• Phenotypes– Females:– Males:

Try these questions on your own:

1. A woman who is heterozygous (a carrier) for colorblindness marries a man with normal vision. What will be the possible phenotype ratio of their children?

2. What is the probability that the sons of a homozygous recessive mother would be colour blind?

*Remember to represent colorblindness with a “-”

More examples of X-linked Recessive Inheritance

• Example #2: Hemophilia

• Hemophilia is a serious ailment in which the blood lacks a clotting factor, and therefore when an individual is injured, they cannot stop bleeding

• About 1 in 4,000 males are born with disorder, much lower incidence in females

Hemophilia Pedigree

Just to make sure you got it! ;)

A woman who is heterozygous for hemophilia marries a normal man:

a. What are the genotypes of the parents?

b. Make a Punnett square for the cross

c. What is the probability that a male offspring will have hemophilia?

d. What is the probability of having a hemophiliac female offspring?

2. X-linked Dominant Inheritance

• X-linked dominant traits are traits that result from the presence of a dominant allele on the X chromosome

• Unlike X-linked recessive traits, females and males both require only ONE dominant allele in order to express the trait

X-linked Dominant Inheritance

• Example #1: Faulty Tooth Enamel and Dental Discoloration

• Individuals who have an X chromosome that carries a dominant allele for this trait will have dental discoloration.

Possible Dental Disorder Phenotypes

X+X+

Female with Dental Discoloration X+X –

Female with Dental Discoloration X -X –

Normal FemaleX+Y

Male with Dental Discoloration X – Y

Normal Male

Let’s think about it...

1. Would a heterozygous woman for dental discoloration display the trait?– Yes, because dental discoloration is a

X-linked dominant trait, so only one dominant allele is needed to express the trait

2. What percentage of the children from a heterozygous mother and an affected father would have dental discoloration?

3. Y-linked Inheritance

• Y-linked traits are controlled by alleles on the Y chromosome

• Another word for Y-linked traits is holandric traits (“wholly male”)

• Are females affected by Y-linked traits?

• Do the words homozygous or heterozygous apply to Y-linked traits?

What do these 2 have in common?

• Example of Y-Linked Inheritance – HAIRY EARS!

• Anthony Victor (India) has hair sprouting from the centre of his outer ears (middle of the pinna) that measures 18.1 cm (7.12 in) at its longest point.

All of the sons of an affected male will display this Y-linked trait

Last Sex-linked Trait Example

Eye color in fruit flies (Drosophilia melanogaster )

• Eye color is controlled by the X chromosome

• Red eyes are dominant to white

• White eyes are most common in males

• Females only display white eyes if they are homozygous recessive for the trait

Fruit Flies Continued

• What type of X-linked inheritance is this?

• Try your new knowledge out on the handout you are about to receive!

X-linked recessive Inheritance because the males show the trait more often that the females. Also, the females must have two X chromosomes, both of which carry the recessive alleles for white eye color in order to have white eyes!

GeneticsQuick Review of Grade 11

Sex Linked TraitsSex Influenced Traits

Polygenic TraitsEpistatic Genes