Incomplete & co-dominance GENETICS Incomplete & co-dominance

Incomplete Dominance Incomplete Dominance occurs when the offspring show a combination of recessive and dominant characteristics Pure Red flowers crossed with White flowers produce all pink flowers in the F1 generation.

All RW (Roan) Offspring are produced Looking at incomplete dominance when pure bred (homozygous) red and white cattle are bred. P1 Red Bull White cow Genotype RR WW R W Gametes F1 All RW (Roan) Offspring are produced

Now what if the F1 generation (all roan) interbred? X RW RW R W gametes F2 RR RW 1 out of 4 Red R 2 out of 4 Roan RW WW W 1 out of 4 White Possible offspring

Co-dominance: Inheritance of Blood Groups The difference in blood groups is due to antigens on the surface of blood cells e.g. “A” blood group has A antigens on the surface of blood cells There are 4 main types of blood group: A; B; AB and O A

Inheritance of Blood Groups Three alleles are involved: A; B and O Alelles A and B are co-dominant over O For example a person with type “A” blood group can have AA or AO genotype If the genotype is AO, the person will have type “A” blood group because the O gene is recessive Note the O allele is a capital letter although it is recessive

Blood Group Genotype A A AA or AO B B BB or BO A B AB AB O OO

Look at the possible blood groups from a male AO and female BO genotypes male gametes A O Blood groups AB; B; A and O are possible B AB BO female gametes O AO OO Possible offspring

Mendel & Dihybrid Cross GENETICS Mendel & Dihybrid Cross

Mendel’s Experiments Gregor Mendel is regarded as the father of modern genetics. His experiments with pea plants has formed the basis of genetics. We will look at one of these experiments with pea plants

Dihybrid Cross This involves the inheritance of two characteristics These characteristics are linked to each other as they occur on the same chromosome

Dihybrid Cross In pea plants, the gene for colour ( Yellow or Green) and the gene for skin type ( Round or Wrinkled) occur on the same chromosome Y Yellow (Y) is dominant Green (y) is recessive Round (R) is dominant Wrinkled (r) is recessive R

What will the seeds of the following look like? Y R Y r y y r y R r Yellow Round Yellow Wrinkled Green Wrinkled Green Round

Pure bred Yellow-Round Seeded plant crossed with Green-Wrinkled Seeded plant PHENOTYPE Y R y r GENOTYPE Y R y r Possible Gametes

Yellow Round Green Wrinkled PHENOTYPE GENOTYPE Possible Gametes OFFSPRING ALL Yellow Round

Now if YyRr is crossed with YyRr female gametes from YyRr yellow,round YYRr YyRR YrRr YYrr yellow,wrinkled YyRr yyRR green,round yyRr Yyrr yyrr green,wrinkled male gametes from YyRr

Here are all the possible types of seed in the F2 generation Try to work out colour and skin of other crosses What seed result when YR and YR gametes fuse? Here are all the possible types of seed in the F2 generation Count the seed the different seed types- How many? yellow, round: yellow,wrinkled: green, round: green, wrinkled: 9 3 3 1 YR Yr yR yr YYRR yellow,round YYRr YyRR YrRr YYrr yellow,wrinkled YyRr yyRR green,round yyRr Yyrr yyrr green,wrinkled

Sex determination & Sex-linked Inheritance GENETICS Sex determination & Sex-linked Inheritance

What are the chances of producing a boy or a girl? SEX DETERMINATION What are the chances of producing a boy or a girl?

Males have an X and a Y chromosome Females have TWO X chromosomes SEX CHROMOSOMES X X X Y Males have an X and a Y chromosome Females have TWO X chromosomes

Males produce X and Y sperm cells by meiosis XY XX Males produce X and Y sperm cells by meiosis X X X X As women are XX, they produce only X egg cells by meiosis

XY XX If an X sperm fuses with the egg cell , it’s a GIRL If an Y sperm fuses with the egg cell , it’s a BOY

X Y X XX XY X XX XY Punnett square of sex determination male gametes X Y X XX XY There is a 50% chance of having a boy or a girl female gametes X XX XY Possible offspring

SEX-LINKED INHERITANCE Y Some Characteristics, like the gene for colour vision are found attached to the X chromosome. This means that the gene for that characteristic is linked to the sex of the individual.

SEX-LINKED INHERITANCE Y In humans, the gene for colour vision is sex-linked. The gene is linked to the X chromosome. The gene for normal colour vision (B) is dominant over the gene for colour blindness (b)

SEX-LINKED INHERITANCE Y If the female parent (XX) has normal vision (BB) and the male (XY) is colour blind (b –only on the X)… How do we link the colour blind genes to the sex chromosomes ?

SEX-LINKED INHERITANCE B B b Y Normal Female BB on the X chromosomes Colour Blind male b on the X chromosome only

Normal Female x Colour Blind Male Y Colour Blind Male Normal Female XBXB XbY Colour blind male possible sperm cells X B X B Normal female possible egg cells Normal Female x Colour Blind Male

Normal Female x Colour Blind Male Y Y Colour Blind Male Normal Female XBXB XbY X B X B X B X X B X B b Y Normal Female but carries the (b) colour blind gene Normal Male Normal Female x Colour Blind Male

Carrier female gametes What are the possible offspring that would result from a carrier female and normal male ? Normal male gametes PHENOTYPE XB Y 1 Normal female 1 2 XB XBXB XBY 2 Normal male Carrier female gametes 3 Carrier female 3 4 Xb XBXb XbY 4 Colour blind male Possible GENOTYPE