Genetics and Inheritance Flashcards
What is a gene?
A gene is a section of DNA, that codes for a specific protein/polypeptide.
What is a genotype?
The genetic constitution of an organism. All the alleles that an organism possesses.
What is a gene pool?
All the alleles within an interbreeding population (at a specific time).
What is a population?
All the individuals of the same species that occupy the same area/habitat at the same time.
What is a phenotype?
The expression of an organism’s genetic constitution and its interaction with the environment.
What is an allele?
Different forms of the same gene.
What is a locus?
Different alleles for the same gene are found at the same position on the homologous chromosome; this position is referred to as the locus of that gene.
What is meant by homozygous?
If the two copies of a gene are the same allele, the organism is said to be homozygous.
What is meant by heterozygous?
The two copies of a gene are different alleles.
What is a dominant allele?
If an allele is dominant, it will always be expressed in the phenotype regardless of whether an organism’s genotype is homozygous or heterozygous
What is a recessive allele?
If an allele is recessive, it will only be expressed in the phenotype if the genotype is homozygous.
What are codominant alleles?
Equally expressed within the phenotype.
What is meant by diploid?
When a cell has two copies of a gene. These may be the same (homozygous) or different (heterozygous).
What is meant by haploid?
When cells only have one copy of a gene, eg. gametes.
What do genetic crosses do?
Show the way in which alleles are passed from one generation to the next.
State three causes of genetic variation.
- Mutation
- Crossing over
- Independent segregation (of homologous chromosomes)
- Random fusion of gametes / fertilisation
What is meant by a genome?
- (All) the DNA in a cell/organism
- The total number of DNA bases in a cell/organism
How do multiple alleles of a gene arise?
- Mutations
- Which are different/at different position in the gene
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why.
- Small sample size
- Fusion/fertilisation of gametes is random
- Linked genes, sex linkage, crossing over
- Epistasis
- Lethal genotypes
What does Hardy Weinberg’s equation predict?
- The frequency/proportion of alleles (of a particular gene)
- Will stay constant from one generation to the next
- Providing no mutation/no selection/large population/population genetically isolated/random mating/no migration
Define gene linkage.
(Genes/loci) on the same chromosome
Define epistasis
The allele of one gene affects or masks the expression of another in the phenotype.
Describe why observed phenotypes don’t match expected values.
- Fertilisation is random OR fusion of gametes is random
- Small population/sample
- Selection advantage/lethal alleles
Rules for dominant alleles.
- Affected offspring must have at least one affected parent
- Unaffected parents only have unaffected offspring
- If both parents are affected and have an unaffected offspring, both parents must be heterozygous
Rules for recessive alleles.
-Unaffected parents can have an affected offspring (if they are both heterozygous)
Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.
- (Recessive) allele is always expressed in males / males have one (recessive) allele
- Females need two recessive alleles
Expected offspring phenotype ratios from heterozygous parents for monohybrid inheritance.
Dominant:recessive
3:1
Expected offspring phenotype ratios from heterozygous parents for dihybrid inheritance.
Dominant : recessive
9:3:3:1
Expected offspring phenotype ratios from heterozygous parents for epistasis.
Dominant : recesive
9:4:3 or 15:1 or 9:7
Expected offspring phenotype ratios from heterozygous parents for autosomal linkage.
Dominant : recessive
3:1 (no crossing over) (no othee pattern other than 4 phenotypes with recombination of alleles)
Explain how a single base substitution causes a change in the structure of a polypeptide.
- Change in (sequence of) amino acid(s)/primary structure
- Change in hydrogen/ionic/disulfide bonds
- Aletrs tertiary/3° structure
