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Genetics. Quick Review of Grade 11 Sex Linked T raits Sex Influenced Traits Polygenic Traits Epistatic Genes. How many chromosomes do humans have?. 46…or 23 homologous pairs. 23 from your mother and 23 from your father. Pairs1 through 22 = autosomal chromosomes.

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genetics

Genetics

Quick Review of Grade 11

Sex Linked Traits

Sex Influenced Traits

Polygenic Traits

Epistatic Genes

how many chromosomes do humans have
How many chromosomes do humans have?
  • 46…or 23 homologous pairs
  • 23 from your mother and 23 from your father
  • Pairs1 through 22 = autosomal chromosomes
  • Which chromosomes determine if you’re a girl or boy?
two types of cells
Two Types of Cells
  • SomaticCells – All body cells,

diploid (2n)

  • Sex Cells – Gametes, haploid (n)

Two Types of Chromosomes

  • Autosomal – All body cells
  • Sex Chromosomes – X and Y
the sex chromosomes
The Sex chromosomes

Its all up to

Dad….

If you get a X

you’re a girl

slide5

The Sex chromosomes

But... If you get a

Y you’re a boy

punnett squares
Punnett Squares

X

X

X

XX

XX

XY

Y

XY

slide7

Phenotype

Genotype

Expressed trait (physical appearance)

The set of genes that an organism possesses

Homozygous

Heterozygous

When two alleles are identical Ex. DD

When the two alleles are different Ex. Dd

Allele

Different forms of the same gene

slide8

Dominant

Allele which controls the characteristic whenever it is present.

BB or Bb

recessive

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

bb

genetics1

Genetics

Quick Review of Grade 11

Sex Linked Traits

Sex Influenced Traits

Polygenic Traits

Epistatic Genes

sex linked traits
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
3 Different Forms of Sex Linked Inheritance
  • X-linked recessiveinheritance
  • X-linked dominant inheritance
  • Y-linked inheritance
sex linked inheritance notation
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
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
1. X-linked Recessive Inheritance

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

are you colorblind
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: 64.

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

x linked recessive inheritance
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
Possible Colorblindness Phenotypes

X+X+

Female with Normal Vision

X+X –

Female with Normal Vision (Carrier)

X -X –

Colour Blind Female

X+Y –

Male with Normal Vision

X – Y

Colour Blind Male

let s try a cross x x x y
Let’s try a cross: X+X–• X+Y
  • Phenotypes
    • Females:
    • Males:
let s try a cross x x x y1
Let’s try a cross: X+X–• X-Y
  • Phenotypes
    • Females:
    • Males:
let s try a cross x x x y2
Let’s try a cross: X+X+• X-Y
  • Phenotypes
    • Females:
    • Males:
let s try a cross x x x y3
Let’s try a cross: X-X-• X+Y
  • Phenotypes
    • Females:
    • Males:
try these questions on your own
Try these questions on your own:
  • 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?
  • 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
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
just to make sure you got it
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
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
X-linked DominantInheritance
  • 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
Possible Dental Disorder Phenotypes

X+X+

Female with Dental Discoloration

X+X –

Female with Dental Discoloration

X -X –

Normal Female

X+Y

Male with Dental Discoloration

X – Y

Normal Male

let s think about it
Let’s think about it...
  • 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
  • What percentage of the children from a heterozygous mother and an affected father would have dental discoloration?
3 y linked inheritance
3. Y-linkedInheritance
  • Y-linked traits are controlled by alleles on the Y chromosome
  • Another word for Y-linked traits is holandrictraits(“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
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.
last sex linked trait example
Last Sex-linked Trait Example

Eye color in fruit flies (Drosophiliamelanogaster )

  • 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
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!

genetics2

Genetics

Quick Review of Grade 11

Sex Linked Traits

Sex Influenced Traits

Polygenic Traits

Epistatic Genes