Genetics Flashcards
Hereditary
the passing of traits from parent to offspring
Genetics
branch of biology that studies the ways in which hereditary info is passed from parents to offspring
Gregor Mendel
monk who began the study of hereditary by carrying out experiments using pea plants
Why were peas useful to study?
Several traits of the peas only existed in two forms, mating can be easily controlled, and peas grow easily/mature fast/produce many offspring
Why can pea mating be easily controlled?
The female and male parts are enclosed within the same flower
How do flowers (peas) fertilize?
Either self fertilize or cross pollination
what is cross pollination?
transferring the pollen from one plant to another flower on a different plant
monohybrid cross
studies inheritance of only one pair of contrasting traits
What did Mendel begin his experiments by using?
a monohybrid cross
True breeding plant
Only produces offspring of the same type
What did Mendel do to ensure that each plant was true breeding?
He allowed each plant to self pollinate for several generations
What is the P generation?
The parental generation, or the true breeding plants that produce more of themselves
What was the F1 generation?
The first filial generation
What did the F1 generation result from?
Cross pollination of the two, different, P generation plants (by Mendel)
What happened to the F1 generation?
They were allowed to self pollinate, resulting in the F2 generation
What were Mendel’s results with the F1 generation?
They all had only one trait. In this example, all the flowers were purple-the white trait had disappeared.
What were Mendel’s results with the F2 generation?
The missing trait had reappeared. (705 purple:224 white) (3.15:1)
What did Mendel’s experiment prove instead?
Peas (and humans) have separate heritable factors for each trait, one from each parent.
What did Mendel disprove with his experiments?
Scientific belief that an offspring’s traits were a blend of the parents.
What are the separate heritable factors for each trait called?
Genes.
How many copies of a gene does an individual have, and where do they get them according to Mendel’s Hypotheses?
An individual has two copies of every gene, one from each parent
What are alleles?
Alternative versions/copies of the same gene
What is the example of an allele in relation to Mendel’s experiment?
Purple vs white flowers
What happens when there are two different alleles in an organism?
Only one will be expressed
What is a dominant allele?
Observable/expressed
What is a recessive allele?
Trait that isn’t expressed in presence of dominant
Which alleles (dominant v. recessive) were present in Mendel’s experiments?
One dominant, one recessive
Did Mendel’s hypotheses include alleles and dominance?
Yes
Gametes formed by meiosis have how many alleles for each trait? Was this mentioned in Mendel’s experiments?
Only one, and yes
What happens to the alleles when gametes unite in fertilization?
Each gamete contributes one allele, their allele
How are dominant alleles represented?
Write the first letter of trait as capital
How are recessive alleles represented?
First letter of dominant trait, but lowercase
Homozygous
Individuals that have two alleles for the same trait
Heterozygous
Individuals that have two different alleles
Which allele is expressed in heterozygous individuals?
Dominant
Phenotype
Appearance
Genotype
Alleles an individual has
What is the law of segregation?
Two alleles separate from one another when gametes are formed
What does the law of segregation explain?
the behavior of chromosomes during meiosis
What are the laws of heredity?
The law of segregation, law of independent assortment
What did Mendel do after studying monohybrid crosses
He investigated whether the inheritance of one trait (like flower color) affected inheritance of a different trait (like plant height)
How did Mendel investigate whether inheritance of certain traits were linked?
He experimented with dihybrid crosses
What are dihybrid crosses?
Crosses that consider 2 pairs of contrasting traits
What is the law of independent assortment?
The inheritance of one trait does not influence others bc the alleles of different genes separate independently from one another during gamete formation
Test cross
an individual whose phenotype is dominant but genotype is unknown is crossed w/ a homozygous recessive individual
Why would one use a test cross?
To know whether an organism w/ a dominant phenotype is heterozygous or homozygous for a trait
How do the results of a test cross exemplify the answer?
If all offspring exhibit this dominant phenotype, the genotype must be homozygous for that allele. If half offspring exhibit both phenotypes, it must be heterozygous.
Incomplete dominance
The inheritance of a dominant trait and a recessive trait results in a blending of traits that isn’t exactly like either parent
Codominance
two dominant traits, both visible
How is codominance often represented?
Capital letters w/ superscripts
How is codominance found in humans?
Blood type-AB
Multiple Alleles
more than 2 possible alleles for a certain trait (individual only inherits two possibilities)
Multiple Alleles-blood type
3 different alleles for blood, a, b, and o, but you can only have 2
What do the A and B alleles code for?
the presence of certain markers on the surface of red blood cells
What does the O allele code for?
No markers
Which blood type alleles are dominant?
A, B
Which blood type alleles are recessive?
O
How does AB phenotype occur?
If both A and B alleles are present, since they’re codominant
Setting up Punnett Square-dihybrid crosses
- determine genotype of parents
- determine possible gametes
- write these gametes on the top and left of a 16sq punnett square
- complete the punnett square
What is an autosome?
A non-sex chromosome
Autosomal trait
A trait located on an autosome
Sex-linked/X-linked trait
trait whose allele is located on the X chromosome
Will a male who carries the recessive allele on his X chromosome exhibit the condition?
Yes, bc he only has one X
Will a female who carries the recessive allele on one of her chromosome exhibit the condition?
No, only if it is on both X chromosomes. Otherwise, she will just carry it.
How can you learn about the chances of passing down a trait within your own family?
A pedigree
Pedigree
family history constructed by geneticists that shows how a trait is inherited over several generations
In what case might a pedigree be helpful?
If the trait is a genetic disorder and the family members want to know if they are carriers, or if their children can get the disorder
How to tell by a pedigree if a trait is autosomal or sex linked?
Sex linked usually appears in more males
How to tell by a pedigree if a trait is dominant or recessive?
Dominance will appear in every generation (usually) while recessive can appear in one, then skip a generation, then appear in a later generation
How to tell by a pedigree if a trait is homozygous or heterozygous?
If the phenotype shows the dominant allele, genotype must be homozygous dominant or heterozygous. If phenotype is recessive, genotype must be homozygous recessive.
Blood type O
ii
Blood type A
IAi or IAIA
Blood type B
IBi or IBIB
What is blood type AB
IAIB
What is dominance in blood type?
A and B over O, codominance together
Polygenic trait
Trait influenced by several genes
Where can polygenic traits be located?
Same chromosome or different chromosomes
Why do many different polygenic combinations occur in offspring?
Independent assortment, crossing over
What can an individual’s phenotype also depend on?
Environmental conditions
