D3.2 Inheritance Flashcards
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Compare and contrast discontinuous and continuous variation
Discontinuous:
- deals with a few clear-cut phenotypes (e.g. double eyelids, eye colour, blood group)
- controlled by a few specific genes
- genes do not show additive effect
- not affected by environemental conditions
Continuous:
- deals with a range of phenotypes (e.g. dark to fair skin, height)
- controlled by many genes
- genes show additive effect
- affected by environmental conditions
Define “P/F1/F2 generation”
P generation: parent generation
F1 generation: First Filial generation/the offspring of the P generation
F2: Second Filial generation/the offsrping of the F1 generation
1 Example of self-pollination in plants
Pollen contains male haploid gametes, ovary contains female haploid gametes.
pea plants have flowers that can produce both male pollen and female ovaries.
- if gamates are prepared at the same time, self-pollination and hence self-fertilisation occurs.
- however this results in less genetic diversity
Define homozygous, heterozygous, and genotype
Homozygous: 2 identical copies of an allele for a gene
Heterozygous: 2 different copies of an allel for a gene
Genotype: the combinaton of alleles inherited by an organism
Differentiate btwn alleles and genes
Alleles are alternative forms of the same gene.
- e.g. different alleles of the gene coding for eye colour gives different eye colours
Suggest examples of phenotypes due to:
1. genotype only
2. environment only
3. interaction btwn genotype and environment
Phenotypes are the observable traits of an organism
Phenotypes due to Genotype only:
- ABO blood type
- genetic conditions such as huntingtons disease (dominant) cystic fibrosis, colour blindness
Phenotypes due to environment only:
- learned behaviour
- aquired physical traits e.g. scars
Phenotypes due to interaction btwn genotype and environment:
- height (while maximum height is limited by genotype, a malnourished person may not reach their full height)
- cancer
Define phenotypic plasticity
An organisms ability to express its phenotype differently depending on the environment
- e.g. a plant activates genes that produce a growth hormone to make leaves thicker when it senses more light is present
Example of a human disease due to autosomal recessive allele
PHENYLKETONURIA
- a recessive genetic condition caused by mutation in the autosomal gene that codes for the enzyme to convert phenylalanine to tyrosine.
- as the automsomal PAH gene is mutated, there are low levels of the enzyme phenylalanine hydoxylase, resulting in higher levels of the toxic amino acid phenylalanine as it is not converted to non-toxic tyrosine
- If there is high quantity of protein in diet, phenylalanine becomes toxic, imparing brain development
= people with phenylketonuria are advised to eat a diet low with phenylalanine, avoiding eggs, chicken etc.
- dietary supplements are needed as these avoided foods are rich in protein and needed for healthy growth and development
Describe the combination of alleles for blood groups in humans
IA = Allele to produce proteins called type A antigens
IB = Allele to produce proteins called type B antigens
i = recessive allele produces neither type A/B antigens
Type A: IAIA or IAi
Type B: IBIB or IBi
Type AB: IAIB
Type O: ii
Differntiate btwn codominance and incomplete dominance, giving an example of each
Codominance:
- heterozygotes have a dual phenotype
- e.g. IAIB alleles producing both A and B antigens, expressing both phenotypes
Incomplete dominance:
- heterozygotes have an INTERMEDIATE phenotype
- e.g. the 4 o’clock flower opens its flowers late in the afternoon
- its alleles for flower colour are CR (red flowers) and CW (white flowers)
- if the combination is CRCW, the resulting flower is PINK, where it is a mix of both parents alleles, where neither allele is masked
How is the sex of a human zygote determined?
(X chromosome is longer than Y chromosome so far more genes are carried by the X chromsome. Both are part of the 23rd pair of chromosomes)
Females have 2 X chromsomes = female gamates only have 1 X chromsome
Males have X and Y chromsome = male gamates have either X or Y chromosome
= the sex of the zygote is dependent on the sex chromsome in the sperm.
Example of sex-linked genetic disorder
HAEMOPHILLIA
- a sex-linked genetic disorder in which blood does not clot properly
= at risk of bleeding to death from minor injuries e.g. a bruise
- the alleles are found only in the X chromsome, where Xh = haemophilia and XH = ability to clot blood
- XhXh = affected female, XhY = affected male
females have a much lower chance of being affected as they have 3 possible genotypes (XhXh, XHXh, XHXH) wherease males only have 2 possible genotypes (XhY, XHY). As females have the chance of being heterozygous (XHXh) where the dominant allele masks the recessive allele, they have a lower chance of being affected
Define polygenic inheritance
when 2 or more genes influence the expression of the same trait
Practice drawing box-and-whisker diagrams from sets of data/worked examples
IQ1: the 25th percentile
IQ2: the median
IQ3: the 75th percentile
The box is btwn IQ1 and IQ3. Use the minimum and maximum values as the whiskers if:
- the values do not differ from IQ1 and IQ3 by (IQ3-IQ1)*1.5. If the values do differ, consider the values to be outliers and take the second lowest/highest value
The box-and-whisker diagram shows us if the values are evenly distributed around the median OR if they are skewed towards one side.
Explain why we can predict the genotypic and phenotypic ratios of 9:3:3:1 and 1:1:1:1. State the types of alleles to be crossed with each other to get these ratios.
Due to Mendel’s law of independent assortment (or Mendel’s second law) which states that each gene is passed on independently of other genes.
- this is due to random orientation during metaphase I and crossing over during prophase I, where the genetic material is shuffled so that when one gene for one trait is passed on to one of the daughter cells, it separates from the other genes
- this law only applies if genes are on different chromosomes OR are far enough apart on 1 chromosome for recombination rates to reach 50%.
9:3:3:1 is from the crossing of a homozygous dominant for both traits (e.g. yellow and round), and a homozygous recessive for both traits (e.g. green and wrinkled.
1:1:1:1 is from the crossing of heterozygous for both traits and homozygous recessive for both traits
