Genetic Crosses Flashcards
Alleles
Different forms of the same gene
Locus
A genes position on a chromosome
Dominant
The allele prevents the recessive allele from working
Recessive
The allele is masked by the dominant gene
Genotype
Genetic make-up of an organism
Phenotype
Physical expression of a gene
Progeny
Offspring
Homozygous
The alleles present are identical
Autosomes
Non-sex chromosomes
Incomplete dominance
~ Neither allele is dominant or recessive
~ An intermediate phenotype is produced
Pedigree studies
A pedigree is a diagram showing the genetic history of a group of related individuals
Sex determination
~ Humans : XX=Female XY=Male
~ Other species (Birds, butterflies, moths) XY=Female XX=Male
Gregor Mendel
Father of genetics
Mendel’s first law - law of segregation
Inherited traits are controlled by pairs of factors. These factors separate during gamete formation. Each gamete contains one factor for each trait.
Mendel’s second law - law of independent assortment
When gametes form, each member of one pair of alleles is equally likely to combine with either member of another pair of alleles.
Linkage
~ Genes found on the same chromosomes
~ Leads to less variation
Sex Linkage
Gene found on the X chromosome
Non-nuclear inheritance
Non-nuclear or extra-nuclear genes are present in the mitochondria and chloroplasts
Monohybrid cross - Example: In pea plants, green pods are dominant to yellow pods.
Show by means of diagrams the genotypes and phenotypes of the F1 progeny that result from crossing two heterozygous plants.
Key: GG=Green, Gg=Green, gg=Yellow
Parents: Gg x Gg
Gametes: G g G g
Genotype: G g
G GG Gg
g Gg gg
Phenotype: 3 Green
1 Yellow
Dihybrid cross - Example : In guinea pigs, black coat is dominant to white coat . Also short hair is dominant to long hair.
Show the genotypes and phenotypes of a cross involving two black-coated, short-haired guinea pigs, heterozygous for both traits.
Key: BB=Black, Bb=Black,
bb=White, SS=Short, Ss=Short,
ss=Long
Parents: BbSs x BbSs
Gametes: BS Bs bS bs BS Bs bS bs
Genotype: BS Bs bS bs
BS BBSS BBSs BbSS BbSs
Bs BBSs BBss BbSs Bbss
bS BbSS BbSs bbSS bbSs
bs BbSs Bbss bbSs bbss
Phenotype: 9 Black and Short
3 Black and Long
3 White Short
1 White Long
Sex-linked - Example: Outline the parents, gametes, genotype and phenotype for the following cross;
Normal male x Heterozygous female
Key: XNXN=Female Normal, XNXn=Female Normal, XnXn=Female Colour Blind, XNY- =Male Normal,
XnY- =Male Colour Blind
Parents: XNXn x XNY-
Gametes: XN Xn XN Y-
Genotype: XN Y-
XN XNXN XNY-
Xn XNXn XnY-
Phenotype: 2 Female Normal
1 Male Normal
1 Male Colour Blind
