Mendelian Genetics Flashcards
What did Mendelian study?
pea plants
Why did Mendelian study peas?
they have short generation time, produce a large number of offspring
What is hybridization?
The cross-breeding of organisms with certain traits to obtain other specific traits
What is a gene?
-genes are alternative versions of traits
-genes are made up of DNA
-multiple genes make up a chromosome
-a gene is the basic functional unit of heredity
What is an allele
-An allele is 1 of 2 or more alternative forms of a gene
-dominant alleles mask the recessive alleles (determines the characteristic)
-2 alleles separate during gamete formation and end up in different gametes
What is a phenotype?
a phenotype is an observable expression of a heritable trait ex) color
What is a genotype?
a genotype is the pattern of heritable alleles ex) PP - homozygous
What is Pp an example of
heterozygous genotype
What is ‘nn’ an example of
homozygous genotype
What is a test cross?
-A test cross can be used when dealing with an unknown genotype
-the genotype can be characterized by a test cross with a known recessive genotype
What are Mendel’s Laws?
- Law of segregation
- Law of independent assortment
What is the Law of segregation?
Law of segregation is when 2 alleles separate during gamete formation and end up in separate gametes.
What is the law of independent assortment?
Law of independent assortment is when each pair of alleles separate independently from any other pair or alleles during gamete formation
-applies to genes that are located on different chromosomes
What does Mendel’s laws assume?
simple inheritance:
-each character is described by 1 gene
-each gene has 2 alleles
-each gene has 1 complete dominant and 1 complete recessive
-each gene is located on a separate chromosome
What are the degrees of dominance?
Incomplete dominance and codominance
What is incomplete dominance?
when neither allele dominates
What is codominance?
when 2 alleles affect the phenotype in separate distinguishable ways
-ex) human blood
Enzymes in Mendel’s peas
R = correct enzyme
r = defective enzyme
rr = peas accumulate excess unbranched starch that causes osmotic swelling and wrinkling when dry
What is pleiotropy?
when one gene produces multiple phenotypes
-ex) pea gene for the flower color also determines the color of the seed coating
What is epistasis?
When the phenotypic expression of 1 gene affects the phenotypic expression of another gene
-ex) Labrador coat color
What is polygenic inheritance?
when 1 phenotype is affected by multiple genes
-ex) height, skin color
What is meiosis?
-ensures that daughter cells inherit different genetic material than parent cells
-consists of 2 consecutive rounds of cell division
1. separates homologous chromosomes into separate cells
2. separates each sister chromatid to produce a haploid gamete
What are chromosomes?
-cellular structures that consist of genes
-follow Mendel’s laws of segregation and independent assortment during meiosis
-Thomas H Morgan showed that they carry genes
What did Thomas H Morgan study?
Drosophila (fruit flies)
What are sex-linked genes?
-sex linked genes are found on sex chromosomes
-show altered inheritance patterns from autosomal genes
What are sex chromosomes?
-determine the sex of the offspring depending on what is passed down
-XX = girl
-XY = boy
-Y can only be passed onto offspring from male
Describe linkages between chromosomes
-genes on the same chromosome tend to be inherited together (linked)
-when 2 genes are linked, their inheritance will assort dependently
Describe recombination
-during meiosis, homologous chromosomes can break and recombine from crossovers
What affects the recombination frequency?
the physical distance on the chromosomes
