6.1.2 Patterns Of Inheritance Flashcards
What are the two types of variation and give an example?
Continuous/ Quantitative - measurable, when individuals in a population vary within a range - there are no distinct categories e.g. height, waist length or fur length
Discontinuous/ Qualitative - not measurable, when there are two or more distinct categories - each individual falls into only 1 of these categories, there are no intermediates e.g. blood group and tongue-rolling ability
Define Phenotype
The physical expression of genotype
Define Genotype
The alleles an organism has
Define Allele
Form of an allele
Define Polygenic and give an example
Inherited characteristics that show continuous variation - influenced by many genes
E.g. Human skin colour is polygenic - comes in a lot of different shades of colour
Define Monogenic and give an example
Inherited characteristics that show discontinuous variation - usually only influenced by one gene ( or a small number of genes)
E.g. violet flower colour (either coloured or white) is controlled by only 1 gene
What 3 factors impact phenotypic variation?
- Genotype
- The Environment
- Genotype and the environment
How does the environment impact phenotypic variation and give 2 examples?
Factors such as climate, food and lifestyle. Characteristics controlled by environmental factors can change over an organism’s life
- Etiolation - when plants grow abnormally long and spindly because they’re not getting enough light
- Chlorosis - when plants don’t produce enough chlorophyll + turn yellow - caused by several environmental factors e.g. lack of magnesium in the soil
How do the environment and genotype, both influence phenotypic variation.
Genotype tends to influence the characteristics an organism is born with but environmental factors can influence how some of those characteristics develop
E.g. Body mass in animals, partly genetic but strongly influenced by environmental factors such as diet
Also Height of pea plants - whether they are dwarf or tall is determined by genotype but the exact height of the tall and dwarf plants varies because of environmental factors e.g. light intensity and water availability
Define a gene
A sequence of bases on DNA molecules that codes for a protein (polypeptide) which results in a characteristic
Define an Allele
Different versions of the same gene
Define Locus
Allele of each gene on a fixed position
Are phenotypes always visible characteristics?
No, as metabolic rate is a phenotype but is not directly visible
Define homozygous and heterozygous?
Homozygous - carries 2 copies of the same allele
Heterozygous - carries 2 different alleles
Define dominant allele
An allele that is always expressed
Define Recessive allele
Alleles which are only expressed when 2 are present
Define Codominant alleles
When both alleles are expressed in phenotype as neither one is recessive
Define a carrier
A person carrying an allele which is not expressed in the phenotype but can be passed onto offspring.
Define Monogenic/Monohybrid inheritance
Inheritance of a characteristic controlled by a single gene
What is the first set of offspring called?
F1 generation
What is second set of offspring called?
F2 generation
What is a dihybrid cross?
When 2 genes are simultaneously inherited, inheritance of 2 characteristics, which are controlled by different genes - each of the 2 genes have different alleles
Define Heterogametic
They have 2 types of sex chromosomes (X AND Y)
Define Homogametic
Only have one kind of sex chromosome (X AND X)
Define sex linkage
Alleles that code for these characteristics are located on the sex chromosome
Why does is the Y chromosome less likely to carry genes?
They are smaller than X chromosomes and thus carry less genes so most genes on sex chromosomes are carries by X chromosome (X linked genes)
Why are males more likely to carry sex-linked related diseases (express sex-linked genes)?
As they only have one X chromosome, they often only have one allele for sex-linked gene as as they only have one copy they express the characteristic even if it is recessive
Define Autosome
Any chromosome that isn’t a sex chromosome
What is linkage on autosomal genes
The genes on the same autosome that stay together during IA and M1 and so their alleles will be passed onto offspring together
What can stop autosomal genes?
Crossing over - the closer the genes are on the autosome the less likely crossing over will split them apart.
How does autosomal linkage impact phenotypic ratios + give an example.
You won’t get the expected phenotypic ratio of offspring of a cross
E.g. an expected ration of 9:3:3:1 of a dihybrid cross of two heterozygous parents will actually result in a 3:1 ratio as the autosomally - linked alleles are inherited together, meaning more offspring will get heterozygous genotype
What is a back cross?
Crossing the offspring with one of the parents
What is Epistasis and give 2 examples?
When the allele of one genes blocks/masks the expression of the alleles of another gene
E.g. Widow’s peak - if one has alleles that code for baldness, it does not matter if person has allele for widow’s peak as you have no hair - the baldness genes are epistatic to the widow’s peak gene
E.g. Flower pigment is controlled by 2 genes, if gene 1 codes for yellow + gene 2 odes for enzyme that turns yellow pigment orange. If one doesn’t have the Y allele it won’t matter if you have R allele or not as flower will be colourless