Inheritance Flashcards
- 1.6 Predict frequencies of genotypes and phenotypes using data from probability models including frequency histograms and by taking into consideration patterns of inheritance for the following types of alleles
- autosomal dominant
- sex-linked
- multiple
Explain genes, genotypes and alleles.
Genes carry information for specific traits. Alleles are alternative forms of a gene located in the same poistion of a homologous chromosome. The gene for eye colour can have a allele for blue eyes or an allele for brown eyes. Although there can be a number of different alleles for a gene, a single individual can only carry two in total (one on each homologous chromosome). If two alleles for a gene in an individual are the same the individual is homozygous. If the two alleles for a gene in one individual are different, the individual is heterozygous for that gene.
- 1.6 Predict frequencies of genotypes and phenotypes using data from probability models including frequency histograms and by taking into consideration patterns of inheritance for the following types of alleles
- autosomal dominant
- sex-linked
- multiple
Contrast genotype and phenotype.
The genotype is the genetic makeup for an individual- it describes the alleles that are present in an individual. The phenotype is the visible trail resulting from the genotype. In situations where one gene is responsible for a trait, one allele may be expressed while the other allele is not evident in the phenotype. In this case, the expressed allele codes for the dominant trait. The masked allele codes for the recessive trait (which is masked by the dominant allele in the heterozygous condition but exppressed in the homozygous condition. Dominant and recessive traits exist when a trait has two different forms at the gene level. The trait that first appears or is visibly expressed in the organism is called the dominant trait. The trait that is present at the gene level but is masked and does not show itself in the organism is called the recessive trait. If this allele is found on an autosome it is referred to as autosomal dominant. A recessive allele found on an autosome is referred to as autosomal recessive.
- 1.6 Predict frequencies of genotypes and phenotypes using data from probability models including frequency histograms and by taking into consideration patterns of inheritance for the following types of alleles
- autosomal dominant
- sex-linked
- multiple
Describe the patterns of codominance and incomplete dominance.
Incomplete dominance occurs when neither allele is completely dominant or completely recessive. It can result in a third phenotype when heterozygous.
RR - red
rr - white
Rr - pink
Incomplete dominance is a form of Gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype. It is also known as partial dominance. Codominance occurs when both alleles are equally expressed. The alleles are usually both written with capital letters to indicate both are dominant.
- 1.6 Predict frequencies of genotypes and phenotypes using data from probability models including frequency histograms and by taking into consideration patterns of inheritance for the following types of alleles
- autosomal dominant
- sex-linked
- multiple
Explain and provide an example for multiple alleles inheritance.
Multiple alleles is a type of non-Mendelian inheritance pattern that involves more than just the typical two alleles that usually code for a certain characteristic in a species. The human ABO blood type alleles/trait is an example of a trait with multiple alleles. There are three possible alleles for blood group, A, B and O. A and B are codominant and O is recessive to the other two alleles.
- 1.6 Predict frequencies of genotypes and phenotypes using data from probability models including frequency histograms and by taking into consideration patterns of inheritance for the following types of alleles
- autosomal dominant
- sex-linked
- multiple
Explain sex-linked inheritance.
Sex in humans is determined by the 23rd pair of homologous chromosome (termed the sex chromosome). When gametes are formed during meiosis, the sex chromosome are separated. All female eggs will contain a X chromosome. 50% of male sperm carry a Y chromosome and 50% carry an X chromosome. Sex linked inheritance involves genes located on the sex chromosomes. Most of these genes are found on the X-chromosome so are referred to as X-linked. Few genes are on the Y chromsome.
4.1.18 Define polygenetic inheritance and predict frequencies of genotypes and phenotypes for using three possible alleles
Define polygenic inheritance.
Variation in phenotypes for a particular characteristic cam be either discrete or continuous. Monogenetic traits (characteristics controlled by a single gene) tend to exhibit discrete variation, with individuals expressing one of a number of distinct phenotypes. Polygenic traits (characteristics controlled by more than two genes) tend to exhibit continuous variation, with individual’s phenotype existing somewhere along a continuous spectrum of possible phenotypes. In the case of polygenic inheritance increasing the number of loci responsible for a particular trait increases the number of possible phenotypes. This results in a frequency histogram that follows a bell-shaped normal distribution curve. Phenotypic characteristics are not solely determined by genotype but are also influenced by environmental factors that can increase the variation in a particular trait. Examples include human
height and skin colour.
Differentiate between polygenic and monogenic traits.
Monogenic traits are traits like face freckles or a cleft chin, which result from the product of a single gene. Polygenic traits are traits such as height or eye color that result from the product of multiple genes. Polygenic inheritance refers to the kind of inheritance in which the trait is produced from the cumulative effects of many genes in contrast to monogenic inheritance in which the trait results from the expression of one gene (or one gene pair).
