Transmission Genetics Flashcards
Describe transmission genetics
How traits/genes are passed from parent to offspring
Define true-breeding/pure-breeding strains
Homozygous organisms that when self-fertilized or intercrossed produce offspring with the same phenotype
ex. PP (purple flowers), pp (white flowers)
Define reciprocal crosses and give an example to clarify
A cross between two different parental phenotypes and a second cross in which the sexes are switched
ex.
cross 1: female with purple flowers (PP) x male with white flowers (pp)
cross 2: female with white flowers (pp) x male with purple flowers (PP)
Define test crosses
crossing an individual with a dominant phenotype but an unknown genotype with a second dominant recessive individual
Define dominant phenotype
The phenotype that is expressed in a heterozygous organism
This would be the same phenotype expressed as in a dominant homozygote
Define recessive phenotype
The phenotype that would only be expressed if an individual was homozygous recessive
Ie., the recessive phenotype is not expressed in a heterozygous individual
Define homozygous genotype
When both the alleles in a diploid genotype are the same
Define heterozygous genotype
When the alleles in a diploid genotype are different
Define dominant allele
The allele that will be expressed in the phenotype of an individual that is heterozygous or homozygous dominant
Define recessive allele
The allele that will only be expressed in the phenotype if an individual is homozygous recessive
Define phenotypic ratio
Give an example
The ratio of offspring that express each phenotype
ex. offspring from a monohybrid cross will have the ratio 3:1
ex. offspring from a dihybrid cross will have the ratio 9:3:3:1
Define genotypic ratio. Give an example
The ratio of offspring that have each genotype
ex. 1/4 heterozygous: 1/2 homozygous: 1/4 heterozygous in a monohybrid cross
Define a monohybrid cross
A genetic cross between individuals that are heterozygous for ONE gene
Describe a monohybrid cross in terms of genotypes and phenotypes (parental, F1, F2) and gametes (parental, F1)
The parental individuals will be true-breeding (ex. GG x gg)
100% of the F1 offspring will express the dominant phenotype and have the heterozygous genotype (ex. Gg)
the monohybrid cross is when the F1 generation is crossed (ex. Gg x Gg)
The F2 generation will result in a 3:1 phenotypic ratio and a 1/4 heterozygous: 1/2 homozygous: 1/4 heterozygous genotype
Gametes:
one parent will give a G and one parent will give a g
The F1 will have GG, Gg, gg, gG
Explain Mendel’s Law of Segregation referencing chromosome behaviour during meiosis
Ensures that each of the 4 gametes produced by meiosis will only receive one type of allele of each gene
Describe the general structure of a eukaryotic chromosome
Chromosomes are condensed chromatin fibres wrapped tightly around specific proteins
Chromatin/chromosomes are very long and thin fibres of DNA and proteins
Describe a gene
A linear sequence of hundreds-thousands of DNA nucleotides located on a chromosome
Genes carry the information cells need to make proteins that express different hereditary traits
Explain the relationship between genes, chromosomes, and DNA
A gene is composed of many DNA nucleotides and is located on a chromosome
Define sister chromatids
During S phase, a single chromosome will copy itself and form a second identical chromosome and they will combine with their genes aligned to form a sister chromatid
Define homologous pairs
During prophase I of meiosis, 2 sets of sister chromatids that have the alleles for the same genes will join via synapsis at their centromeres to form homologous pairs
2 sets of sister chromatids joined - one sister chromatid will have one allele of a gene and the second sister chromatid pair will have the other allele for the same gene
Describe the cell cycle
a cycle of events that occur in order from the formation of a new cell to the division of that cell into new cells
Describe mitosis and state it’s functions
a type of cell division that occurs in diploid or haploid somatic (body) cells and generates 2 new identical cells
functions:
- asexual reproduction
- growth
- cell replacement
Describe meiosis and state its functions
a type of cell division that occurs only in diploid gametes (sex cells) and generates four genetically unique haploid cells
functions in sexual reproduction and is responsible for genetic diversity
Why does the S phase of interphase precede mitosis and meiosis I but not meiosis II?
S phase is necessary to begin cell division because individual chromosomes must be duplicated in order for there to be enough genetic information for cells to divide into new functioning cells
Not necessary for meiosis II because there is already enough chromosomes to do a division a second time
Describe the steps of meiosis I
G1: chromatins condense into chromosomes
S: chromosomes duplicate and form sister chromatids
prophase I: sister chromatids form homologous pairs
metaphase I: homologous pairs align randomly along the metaphase plate
anaphase I: homologous pairs are pulled apart to the opposite poles
telophase I & cytokinesis: cytoplasm divides and 2 cells form with different sister chromatids
Describe the steps of meiosis II
In each of the two cells:
Sister chromatids align randomly on the metaphase plate in metaphase II
Sister chromatids are pulled apart to either pole in anaphase II
The two cells divide into two each (total 4) in telophase II and cytokinesis
Describe independent assortment
Independent assortment during metaphase I is when the homologous pairs align along the metaphase plate independently from one another
Describe segregation
Segregation of homologous pairs occurs during anaphase I of meiosis when they are pulled from the metaphase plate into either pole. This will ensure that only one allele of each gene is distributed into each gamete.
Define synapsis
the pairing of two sister chromatids to form a homologous pair during prophase I
What is the purpose of synapsis?
to allow for crossing over
When does crossing over happen?
prophase I
Define synaptonemal complex / what is the purpose of this?
protein structure that forms between homologous chromosomes during prophase I
allows for chromosome pairing, synapsis and crossing over
describe crossing over
during prophase I, sister chromatids join by synapsis to form homologous pairs and can exchange genetic material with each other
Describe chiasmata
the location where homologous pairs are attached
