biology: introduction to genetics Flashcards
WHAT IS GENETICS?
Understanding how characteristics are transmitted from parents to offspring
Began with Gregor Mendel
-1800s monk
- Researched pea plant heredity using observations and statistics
– Discoveries made apply to all organisms
what is heredity?
Passing of traits from parents to offspring
what did mendel do?
Studied seven traits of peas
trait
genetically determined variant of characteristic
how did mendel study his plants?
pollination experiments
pollination
Pollen from anther () transferred to ovary ()
self-pollination
Pollen and ovary from same plant
cross-fertilization
Pollen and ovary from different plants
true-breeding plants
All self-fertilized offspring have same trait as parent
what were Mendel’s conclusions?
- Pair of alleles controls each trait
- Law of Segregation
- Law of Independent Assortment
allele
different forms of a gene
gene
segment on DNA on chromosome that controls trait
dominant allele
hides the recessive trait
recessive allele
no observable effect on organism if dominant allele is present
law of segregation
Paired alleles segregate during meiosis
• Gametes receive one allele from each pair
law of independent assortment
- Alleles sort independently during meiosis
* Genes for one trait do not influence inheritance of genes for another trait
Molecular genetics
Study of structure/function of genes & chromosomes
are all of mendels discoveries still true?
supported by current molecular genetics
each gamete has 1 allele for a gene
each somatic cell has 2 alleles for each gene
dominant allele
capitol letters
recessive alleles
lower case letters
phenotype
Organism’s traits that are expressed
genotype
Organisms genetic makeup; consists of alleles
homozygous
When both alleles are alike
Ex. PP = homozygous dominant (purple flowers)
pp = homozygous recessive (white flowers)
heterozygous
When both alleles are different Ex. Pp = heterozygous Since purple (P) is dominant, plant is purple
can predictions be made about genetics of offspring?
yes using probability
probability
Likelihood that a specific event will occur
punnet square
Diagram used to predict genetics of offspring
Monohybrid cross
only one trait is tracked
testcross
Individual of unknown genotype is crossed with homozygous recessive
• Based on probability, can determine unknown genotype
Ex. Purple (P?) crossed with white (pp)
If no white offspring, what is genotype?
probably PP
If white offspring,
must be Pp
dihybrid cross
Two traits are tracked instead of one.
what are non-mendelian genetics?
genetics that do not follow mendel’s laws
- incomplete dominance
- multiple alleles
- codominace
- polygenic traits
- sex-linked inheritence
incomplete dominance
Heterozygote phenotype is combination of parental phenotypes red snapdragon (CRCR) x white snapdragon (CWCW) 100% offspring are pink(CRCW)
multiple alleles
A gene with two or more alleles
Ex. Blood type A, B, AB, or O
codominance
Both inherited alleles are completely expressed
Ex. Roan coat in cattle
polygenic traits
Traits produced by many genes
Ex. Skin color
sex-linked inheritence
based on sex chromosomes
sex chromosomes
Responsible for determining sex
XX – females; XY - males
Y-linked genes
On the Y chromosome
Very few genes
Mainly code for testes and sperm development; testosterone
X-linked genes
On the X chromosome
Males-
Since only one X, get whatever is on X chromosome
Females-
Since two Xs, dominant and recessive come into play
carrier
Heterozygous for recessive disorder
• Show no symptoms, but may pass recessive allele to offspring
is it a problem to have 2 Xs in females?
no; in fetus cells randomly switch off one chromosome or the other
are some genes inherited together? why?
yes! Linked genes
Genes that tend to be inherited together because they are
located close together on the same chromosome
how do you tell how far apart genes are on chromosome?
Genes far apart on a chromosome are more likely to crossover.
Use crossover frequency to create a genetic map.
what else impacts phenotype?
- Environmental conditions like pH
- Sunlight
- Temperature
- Diet