Inheritance Flashcards
What is a gene?
A gene is a section of DNA that codes for the production of one polypeptide, e.g. the gene for fur colour in rabbits.
What are genetics?
The study of the way in which an organism inherits characteristics from its parent.
What is monohybrid inheritance?
Inheritance of a single characteristic, controlled by one gene (each parent has 2 alleles for the gene, one on each chromosome of a pair).
Greg Mendels pea experiment?
Investigated inheritance in peas because:
Easy to grow
Flowers self-fertilise and cross-fertilise.
Flowers are fruit and flowers in same year.
Make large number of seeds.
He chose 3 contrasting characteristics and found:
Controlled by single genes.
Controlled by genes on different chromosomes.
Clear cut and easy to tell apart.
What was Mendels first law called?
The law of segregation.
What does the first law say?
“The characteristics of an organism are determined by factors (alleles) which occur in pairs. Only one of a pair of factors can be present in a single gamete”.
What is an allele?
An allele is a version of a gene, e.g. black fur or white fur
What is a genotype?
It is the alleles that an organism has for a characteristic, e.g. BB, bb, Bb.
What is a phenotype?
It is the observable characteristic of an organism due to its genotype, e.g. back fur or white fur.
What is a homozygous organism?
If it only has one type of allele present in its genotype for that characteristic, e.g. BB or bb.
What is a heterozygous organism?
If it has two different alleles present in its genotype for that characteristic, e.g. Bb.
What is a dominant allele?
The one that shows itself in the phenotype of an organism whose genotype is heterozygous for that characteristic.
What is a recessive allele?
The one that does not show itself in the phenotype of an organism whose genotype is heterozygous for that characteristic.
Some definitions!!
P= parental generation
F1= first filial generation (offspring from p).
F2= second filial generation (offsping from f1).
What does a genetic cross show?
The generations. Genotypes of parents and offspring. Phenotypes of parents and offspring. Alleles present in the gametes. Symbols for the alleles are defined.
Rules for a genetic cross??
Both parents donate 1 copy of a gene to each offspring.
Characteristic appearing in pehotype must have 1 allele in genotype.
Recessive characteristic is homozygous to be expressed in phenotype.
If 2 parents show charactistic not shown in offspring, both parents are carriers and offspring is homozygous recessive.
Instructions for writing a genetic cross?
- Choose suitable symbols for alleles, eg. single letters, make sure upper and lower differ in shape+size.
- Write parents genotypes with the appropriate pairs of letters.
- Show gametes produced by parents, circle them.
- Use a punnett square, to show possible combinations from random crossing.
- Indicate the ratio of the phenotypes.
Test cross or back cross?
To tell is a dominant phenotype individual is heterozygous or homozygous, it may be crossed with the homozygous recessive.
If unknown is homozygous dominant, all offspring have dominant phenotype.
If unknown is heterozygous, half offspring have recessive and half will be dominant.
What is sex-determination?
Humans have 23 pairs of homologous chromosomes in diploid body cells.
23rd pair are the sex chromosomes, gender.
Other 22 pairs are AUTOSOMES.
Males have X and Y chromosomes, after gamete formation half sperm have X and half have Y.
What is co-dominance?
Both alleles are equally dominant so both alleles express themselves equally in the phenotype of a heterozygote.
Heterozygotes show a phenotype intermediate between those of the 2 homozygotes.
What is incomplete dominance?
The phenotype of the heterozygote is intermediate betwen the 2 parental phenotypes, rather than both being expressed, e.g. red and white makes pink.
Neither the allele for red flowers or white are dominant so no upper or lower case.
What are dihybrid crosses?
Looks at the inheritance of 2 characteristics (from 2 different genes), assumption is the 2 genes are carried on different pairs of homologous chromosomes and so independently sort during gamete formation.
What is dihybrid inheritance?
The inhertiance of two seperate genes each on a different pair of homologous chromosomes.
What is autosomal linkage?
Looks at the inheritance of 2 characteristics (from 2 different genes), genes are carried on the same pair of homologous chromosomes so cannot independently assort during gamete formation. Giving different ratios of offspring.
Said to be LINKED..
