Mendelian Genetics 2 Flashcards
Meiosis Chromosomal basis of inheritance Non-mendelian patterns of inheritance Incomplete dominance Co-dominance Multiple alleles Pleiotropy Epistasis Polygenic inheritance Environment
What is the chromosomal basis of inheritance?
46 chromosomes - 23 pairs of homologous chromosomes
22 pairs of autosomes, 1 pair of sex chromosomes
What is mitosis and what does it produce? (2)
Process where cells are replicated for growth and repair
Produces 2 daughter cells, each diploid with 2 sets of chromosomes each
What is meiosis and what does it produce? (2)
Process by which gametes are reproduced
Produces 4 daughter cells each haploid containing a single set of chromosomes
Describe the stages in meiosis 1:
Interphase 1 - chromosomes duplicate
Prophase 1 - Homologous chromosomes pair and exchange segments (crossing over)
Metaphase 1 - Tetrads line up on the equator
Anaphase 1 - Pairs of homologous chromosomes split up
Telophase 1 - 2 haploid cells form, chromosomes are still double - cytoplasm divides
What is a summary of meiosis 1 and 2:
meiosis 1 - homologous pairs are separated by reducing chromosome number by half
Meiosis 2 - Equational division, sister chromatids are separated producing 4 haploid gametes
Describe the stages in meiosis 2:
Prophase 2 - spindle forms around the chromosomes
Metaphase 2 - Chromosomes line up in the centre
Anaphase 2 - The spindle begins to pull them apart
Telophase 2 - Haploid daughter cells forming single chromosomes, cytoplasm divides
Why do we not have the exact same genetics as our parents? (2)
Independent assortment emit of chromosomes - combinations differ from parents
Crossing over means each chromosome isn’t fully maternal or paternal
What is crossing over? (3)
Occurs in prophase 1 of meiosis when. the chromosomes line up
Produces recombinant chromosomes
Average of 1-3 crossing over events per chromosome pair
What is the number of potential combinations from random fertilisation?
2^23 x 2^23 = 70 trillion diploid combinations
What is the law of segregation?
The 2 alleles for each gene segregate during gamete formation. Both the same
What is the law of independent assortment?
Alleles of genes on non homologous chromosomes assort independently during gamete formation. Both different
What are the non-mendelian patterns of inheritance? (2)
Genotypic ratios follow Mendel’s law but phenotypes do not
Mendel’s laws do not apply
What is incomplete dominance?
The phenotype of a heterozygote is intermediate between the phenotype of the dominant and recessive traits, blending (wavy hair)
What is co-dominance? (2)
When both alleles for a trait are expressed in heterozygous offspring
2 dominant genes are expressed at the same time (blood groups)
What are multiple alleles? (2)
Most genes exist as more than 2 alleles
Multiple alleles and multiple phenotypes
What is pleiotriopy?
Multiple phenotypic traits are affected from one gene
Cystic fibrosis, sickle cell anaemia
What is epistasis?
Phenotypic expression of gene at one locus affects another gene at a different locus
What is polygenic inheritance? (4)
One character influenced by many genes
Generally quantitative traits - continuous variation
Opposite of pleiotropy
Height, skin colour
Where does Mendel’s laws not apply? (3)
Mitochondrial DNA - solely inherited from the maternal line
Linkage - 2 genes that close together physically tend to be inherited together
Linkage disequilibrium - 2 alleles that are not inherited separately
