D3.2 Inheritance Flashcards
[D3.2.1] Define gametes and zygotes
Gametes are haploid (contain 1 copy of each autosomal gene) and these are passed on from parents to offspring as a means of inheritance. This pattern of inheritance is common to all eukaryotes.
[D3.2.2] Describe the 2 methods which can be used to investigate patterns of inheritance in flowering plants
2 species of known flowers can be bred by using a paint brush to directly transfer pollen from the anther of one plant (male part) to the stigma of the other plant (female part). Or, the pollen from the anther can be transferred to the stigma of the same plant, resulting in self-pollination and self-fertilisation. When male gametes in the pollen are carried down the ovary and fuse with female gametes, this forms zygotes that each form inside a seed.
[D3.2.2] Outline the different generations
The parents of known genes are the P generation and the offspring inside the seed are F1 generation. Offspring of F1 are the F2 generation.
[D3.2.3] Define alleles for genotype
Alleles allow different version of the gene to exist. Different alleles are created due to mutation of one base or large sections. Humans have diploid cells with 2 alleles of most genes - 1 inherited from the mother and 1 from the father. Thus the 2 alleles may be identical or different - it may be DD, Dd, or dd. If the alleles are the same, they are homozygous (pure-breeding), whereas if the alleles are different, they are heterozygous. This combination of alleles are known as the genotype.
[D3.2.4/ D3.2.5] Define phenotype and the cause of different phenotypes. Provide examples.
The phenotype of an individual is its observable traits or characteristics. “Observable” means that the trait is visible (like hair colour) or detectable with tests (like could-blind). If an individual is heterozygous, the dominant trait masks the recessive trait, thus it has the same phenotype as homozygous dominant allele, but can produce offspring that are homozygous recessive
Phenotypic traits can be due to the genotypes only, the environment only, or the combination of both:
- Genotypes only: eye colour, haemophilia (blood clotting too slowly)
- Environment only: scars, tattoos
- Environment and genotype: height, autism, diabetes
[D3.2.6] Describe phenotypic plasticity
Phenotypic plasticity is when there is a change in phenotype due to environmental effects, but it is not passed on the generation since the genotype is not affected. Organisms can have varying patterns of gene expression depending on the environment. This is because organisms adapt, resulting in their traits to change. However, it is reversible across generations since the genes have only been turned on or off for the individual, and new alleles have not been made.
[D3.2.7] Outline what PKU is and how it is inherited to an individual. Discuss the chance of developing PKU
Phenylketonuria (PKU) is a recessive genetic condition by mutation in an autosomal gene that codes for the enzyme needed to convert phenylalanine to tyrosine. Therefore, this disease only develops in individuals with 2 copies of the recessive allele. If an individual is heterozygous, they are carriers, meaning that they do not show the characteristics of PKU but can lead to their offspring to develop PKU. Since autosomal genes are affected, there is a 25% chance of developing this disease for both females and males.
[D3.2.8] Describe gene pool and single-nucleotide polymorphism (SNP)
A gene pool is all the genes of all the individuals in a sexually reproducing population. Every new individual receives a maximum of 2 alleles of each gene from the gene pool, and the gene pool can change through evolution overtime.
Positions in a gene where different bases can be present are called single-nucleotide polymorphisms (SNP). Even within one gene, there can be many different positions with SNPs, thus leading to many different alleles of a gene to be present.
[D3.2.9] Describe an exmple of a human trait that has multiple alleles
The ABO blood groups are an example of multiple alleles.
- Blood type A: IAIA / IAi
- Blood type B: IBIB / IBi
- Blood type O: ii
- Blood type AB: IAIB
Where IA and IB are dominant over i
IA nor IB are dominant over the other allele
The different blood types are due to different glycoproteins, that act as antigens, being presented on the plasma membrane of red blood cells. Therefore, blood type A produces anti-B antibodies, and blood type B produces anti-A antibodies. Blood type AB produces both antibodies whereas blood type O does not produce any.
[D3.2.10] Outline codominance and incomplete dominance with examples
Codominance: heterozygous organism have a dual phenotype (shows both characteristics of alleles)
- Ex. Blood type AB have both A and B glycoproteins
Incomplete dominance: heterozygous organism have an intermediate phenotype (mix of both alleles)
- Ex. Marvel-of-Peru, a flower, can either show the colour red, white or an intermediate phenotype of pink
[D3.2.11] Describe how sex of an individual (even with disorder) is determined by outlining X and Y chromosomes.
Sex is determined in humans by the 23rd pair of chromosomes. The different types of sex chromosomes are:
- X chromosome: relatively large and has a centromere at the middle. It contains far more genes than the Y chromosome, and is essential for females and males - both genders have at least one X chromosome.
- Y chromosome: much smaller and has a centromere at the end. It is required for male development.
Therefore, females typically have XX chromosomes while males have XY chromosomes. The other 22 pairs of autosomal chromosomes do not affect the offspring’s gender. When zygotes are formed, a X chromosome is always inherited by the mother, however, the males either pass on their X or Y chromosome in sperm. The Y chromosome is what determines if testes are developed or not. Therefore, even though there are sex chromosome abnormalities like having 2X and 1Y (Klinefelter’s syndrome) or only 1X (Turner’s syndrome), the presence of the Y chromosome determines the gender of the offspring.
[D3.2.12] Describe how sex linked genetic disorders occur with an example and discuss the chance of females and males getting the disorder.
Sex linked genetic disorders are mostly due to recessive alleles of genes and it is often located on the X chromosome that contained many more genes than the Y chromosome. Therefore, if the male’s only copy of the X chromosome has the recessive allele, they have the disorder. On the other hand, females are less likely to have sex linked disorders since both of their X chromosomes must be recessive to have the disorder.
Haemophilia is an example of sex linked disorder that results in individuals to have a lack in a clotting factor protein. Therefore, cuts and other wounds bleed for much linger than a normal person, and internal bleeding occurs frequently. The gene for this clotting factor protein is located on the X chromosome and the allele that causes haemophilia is recessive.
[D3.2.13] Discuss the reason for many people not suffering from disorders and why marriages between siblings and close relatives are prohibited
Even though there are thousands of genetic disorders, most offspring do not suffer from these disorders. This is because these disorders are mostly caused by very rare recessive alleles, and even more rare to inherit 2 alleles of these gene, 1 from each parent. If the parent has a rare allele, this may be passed down the generations, increasing the chance of genetic diseases if marriages occur between siblings and close relatives.
[D3.2.13] Outline the shapes and colours used in pedigree charts
Pedigree charts can be used to deduce the patterns of inheritance:
- Males are shown as squares, females are shown as circles
- Shaded shape indicate that the individual is affected
[D3.2.14] Describe the 2 type of variation that can occur to allow same species to differ in many traits
- Continuous variations (ex. Skin colour)
Skin colour can vary depending on the environmental factor, sunlight. Sunlight stimulates the production of melanin which is a black pigment that increases the protection from UV radiation. The amount of melanin varies continuously, thus resulting in a continuous range of skin colours to be present. Excluding the environmental factor, the trait can also be influenced by multiple genes, thus it is an example of polygenetic inheritance.- Discrete variation (ex. ABO blood types)
ABO blood types are not influenced by environmental factors, but depends on the inherited genes. Since there are 4 distinct types of blood, they are discrete variation that lack in intermediates between them.
- Discrete variation (ex. ABO blood types)
[D3.2.15] State the equation for IQR and outlier
Interquartile range (IQR) = Q3 - Q1
If data point is 1.5 x IQR is above Q3 or below Q1 = outlier
[D3.2.16] Describe segregation and independent assortment for unlinked genes
Segregation is separation of alleles of a gene, so that one of the alleles is inherited. This is needed for a diploid cell to be turned into a haploid gamete.
Independent assortment is the combination of random maternal and paternal chromosomes. Therefore, independent assortment occurs for unlinked gene since they are either on different chromosomes or because they are far enough apart on the same chromosome. Segregation and independent assortment are the consequences of event in meiosis.
[D3.2.17] Outline dihybrid crosses and what Mendel proved through this methods
Dihybrid crosses investigate the joint inheritance of 2 genes. Mendel performed dihybrid crosses where he crossed pure-breeding round yellow peas with pure-breeding wrinkled green peas, which he developed through self-pollination. He found that all F1 hybrids had round yellow peas, showing how the offspring had one of the parent’s phenotype but not the other, further suggesting that there traits are dominant alleles. When Mendel allowed F1 plants to self-pollinate, there were 4 different phenotypes in F2 generation.
The ratios of 9:3:3:1 and 1:1:1:1 are based on Mendel’s second law, which states that each gene will be independent of other genes during sexual reproduction - independent assortment.
[D3.2.18] Outline locus
Locus of a gene is its specific position on one of the autosomes or one of the sex chromosomes. Since there are thousands of genes in the human genome that codes for amino acid sequence of a polypeptide, each of these genes has a characteristic base sequence, varying between the alleles and a locus.
[D3.2.19/ D3.2.20] Outline gene linkage and how they are determined
Gene linkage is when 2 or more genes are located close together on a chromosome, hence resulting in those genes to be inherited together since they fail to independently assort during meiosis. An indication whether genes are linked or not is that F2 ratio will significantly differ from the expected ratio for unlinked genes assorting independently. Autosomal gene linkage is more common than sex linked genes.
[D3.2.19/ D3.2.20] Describe the role of meiosis in producing recombinants
A recombinant is an individual with a different combination of alleles and therefore, different traits from their parents. Recombinants form during meiosis where the random orientation of bivalents results in new combinations of unlinked genes by independent assortment. Crossing over produces new combination of linked genes.
[D3.2.21] Outline chi-squared and its formula. State the null and alternative hypothesis
Chi-squared formula can be used to see if the obtained data is significant. The statistical value obtained from the chi-squared formula can either support the null hypothesis or the alternative hypothesis.
Chi-squared = (Observed−Expected)^2/Expected
H0 (null hypothesis): there is no statistical difference between the observed and expected ratios of the traits.
H1 (alternative hypothesis): there is a statistical difference.
