Biology - Inheritance Flashcards
What is inheritance?
The transmission of traits from one generation of organisms to the next. The offspring resemble their parents.
What is genetics?
The science of heredity and hereditary variation. It studies the similarities and differences between parents and their offspring.
What are genes?
Segments of DNA that codes for a particular characteristic. Offspring resemble their parents because they inherit genes from them. Each gene is a heritable factor, a small segment of DNA on a chromosome that controls a particular characteristic/inheritable feature.
What is a gene locus?
The particular position where a gene is located on a specific chromosome.
What are alleles?
The alternate form of the same gene, and they occupy the same positions on a pair of homologous chromosomes. They can be either dominant or recessive. In a pair, the gene that expresses itself is the dominant allele, and the other is the recessive allele.
What are the characteristics of homologous chromosomes?
Of similar length, similar shape and size, same sequence/position of genes, and centromeres at the same position.
What is phenotype?
The expressed trait or characteristic of an organism that arises from its corresponding genotype.
What is genotype?
The genetic makeup or combination of alleles for a particular gene.
What is homozygous in terms of chromosomes?
Having two identical alleles of a particular gene (e.g. DD or dd) on a pair of homologous chromosomes. When identifying chromosomes, write ‘homozygous dominant’ or ‘homozygous recessive’.
What is heterozygous in terms of chromosomes?
Having two different alleles of a particular gene on a pair of homologous chromosomes. (e.g. Dd)
What do chromosomes comprise of?
One molecule of DNA wrapped around proteins called histones to form chromatin thread. It may carry many genes along its length. Genes code for proteins –> responsible for determining the phenotype of the organism.
What is the relationship between chromatin and chromosomes?
During cell division, chromatin condense into chromosomes.
What are chromosome numbers and its characteristics?
No. of chromosomes in a cell.
- Each species has a fixed chromosome number
- Conserved throughout generations
- Varies from species to species
What are ploidy?
No. of sets of chromosomes present in an organism. (relates to no. of alleles present in a genotype)
How do you draw a genetic diagram?
- Define alleles (if necessary)
- State parental phenotypes then genotypes
- State the gametes (CIRCLED)
- Derive genotypes and phenotypes of offspring (use a Punnett square is needed)
- State all possible gametes produced by F1
- Perform the second genetic cross - state genotype and phenotype of F2
- State the phenotypic ratio of F2 generation phenotype
What is codominance? How is it represented?
Both alleles express themselves in the heterozygote, which expresses a phenotype intermediate between that of its pure-bred parents. They are represented by a capital letter for its gene + different superscript capital letters to represent the different alleles. (e.g. pure bred white + red flower –> pink flower) The F2 generation has a typical phenotypic ratio of 1:2:1
What is multiple alleles?
More than 2 alleles for a particular gene. E.g. ABO blood type.
How are genotypes for blood types written?
Capital letter ‘I’ to represent the gene. The allele for A and B (both codominant) is represented in capital superscript ‘A’ and ‘B’. The ‘O’ blood type is represented by lowercase ‘i’ as it is recessive to both A and B.
How is sex determined in humans?
Presence of sex chromosomes in the genetic makeup. Females possess 2 X chromosomes, and males 1 X and 1 Y. The sex of the child depends on which of the two types of sperm fertilises the egg. (50/50)
What are the characteristics of the chromosomes in a human karyotype?
- 1 pair of sex chromosomes and 22 pairs of autosomes.
- Autosomes code for the proteins needed for other body functions.
- Males and females have different pairs of sex chromosomes but the same types of autosomes.
- Y chromosome has a shorter length than X chromosome. X chromosome carries more genes.
What is a test cross?
Used to determine the presence of the recessive allele in a genotype of an organism, using an organism showing the dominant trait. The process is to mate the suspected hetero/homozygous with a homozygous recessive for the trait and the phenotype of offsping are observed. If all offspring express the dominant trait, the tested parent is homozygous dominant. If half the offspring express the dominant trait, the tested parent is heterozygous.
