Genetics Beyond Mendel     

Types of Dominance1. Complete

-1 gene masks the other (Tt…see Mendel)

2. Incomplete -Neither gene is dominant,

neither is recessive.-The gene effect is mixed-We use 2 different letters for

the homologous pair since neither is dominant.

Use a punnet square to predict offspring!

RW RW

RW RW

R R

W

W

TRY ME! Page 179 #8

Note: Use ‘W’ for white…not ‘b’!

100%

PINK!!!

Red Flower – RR White Flower - WW

Types of Dominance3. Co-Dominance

-Neither gene is dominant or recessive-Gene effects are not mixed-Both genes are expressed at the same

time!-Eg. Roan Cattle – Red hairs and white hairs

LOOK AT ME…I’M ROAN!

Co-Dominance Cont.-Write C (for co-dominance) and a super script (R=Red, W=white)-Red haired = CRCR

-White haired = CWCW

-Red and White (Roan) =CRCW

Use a punnet square to predict offspring:

1) Cross a white cow with a red bull

X

CRCW CRCW

CRCW CRCW

CR CR

CW

CW

2) Cross a white cow with a roan bull

100% Roan!!

A Special Case – Blood Type

• There are three alleles! A B O• A and B are co-dominant• O is recessivePredict offspring bloodtypes for: a) Heterozygous type A mother,

type O father

Blood Type… Cont.

AO OO

AO OO

A O

O

O

b) Mother: AB; Father: Hetero type B

c) Do Page 179, #9

50% AO

50% OO

Predicting Gender

Two sex chromosomes determine gender:

X & Y

Female Genotype: XXMale Genotype: XY

Predict the probability of a couple having a boy!

50% chance of having a boy!

50% chance of having a girl!

Chew on this! Page 184, #12!

X-Linked Traits

•All genes found on the ‘X’ chromosome are “linked”.•Many of the genes on the ‘X’ are not on the ‘Y’.•The ‘X’ is larger and has many genes that are not related to gender… (i.e. colour vision, blood clotting etc.)

Are you colour blind?

WHAT DO YOU SEE?

X-Linked Traits•If a recessive gene is on the ‘X’:-In males it will always be expressed since there is no homologous pair on the ‘Y’.-Therefore (sorry guys) recessive, X-linked diseases are much more common in males!

Hemophilia – I can’t stop bleeding!!

Since gender and the gene are important, both must be noted.

•Dominant allele – H•Recessive allele – h•XH – dominant gene on ‘X’•Xh – recessive gene on ‘X’•Y – no gene on the ‘Y’

Hemophilia

• Female genotypesXHXH – NormalXHXh – Normal but a ‘Carrier’

XhXh – Hemophiliac (very rare)• Male genotypes XHY – Normal XhY - HemophiliacPredict the offspring for: -Mother carrier and a normal father!

• Try these! Page 200, Question 8, 9, 10 (a-f)