genes Flashcards
where are genes contained
chromosomes
who discovered genes
Gregor mendel
what did Gregor Mendel study?
pea plants
overview of gregor mendels experiment
Record parent traits; prevent plant from self-fertilizing; fertilized from another plant; collected seeds; record traits of offspring
medel crossed bred….
true breeding varieties
Mendel’s pea generations:
P generation: cross true breeding parents called hybridization
F1 generation: first offspring
F2: offspring of offspring
what happens to genetic material during fertilization?
material from both parents combine during fertilization
what is a gene?
instructions about something (about a trait) does not say what instructions are, just what they are about.
alleles
different versions of a gene; what instructions actually say
dominant alleles
(capitalized): trait can be seen with only 1 copy of the allele
recessive alleles
(lower cased): trait can only be seen if a dominant allele is NOT present
law of segregation
alleles separate when gametes are formed
homozygote
2 copies of same allele
heterozygote
2 different alleles
genotype:
genetic composition of an individual
phenotype:
physical characteristics of an individual
monohybrid cross: P generation
homozygous dominant or recessive (YY or yy)
monohybrid cross: F1 generation
Genotype? Phenotype?
Genotype: 4 heterozygous (Yy)
Phenotype: 4 dominant (color of Y trait)
monohybrid cross: F2 generation
Genotype? Phenotype?
-Genotype:
*1 homozygous dominant
*2 heterozygous
*1 homozygous recessive
-Phenotype:
*3 dominant
*1 recessive
test cross reveals…
genotype that created that phenotype
dihybrid cross looks at…
2 characteristics at once
dihybrid cross: P generation
*Dominant genotype for both traits
*Recessive genotype for both traits
dihybrid cross: F1 generation
heterozygous for both traits
dihybrid cross: F2 generation
9:3:3:1 phenotype ratio
multiple alleles
genes can have 2+ alleles
(Can still follow dominant/recessive pattern (can have more than 1 recessive pattern)
incomplete dominance
one allele is not completely dominant
*Heterozygotes have intermediate traits
*Both alleles partially expressed
codominance
neither allele is dominant or recessive
Both alleles are expressed in heterozygotes
pleiotropy:
genes often affect more than one trait
example of pleiotropy
friendly foxes bread to be friendly also became cuter (on accident): had more juvenile characteristics such as larger eyes, bigger ears, and a “cuter” look.
epistasis
phenotype of one gene can block phenotype of different gene
*One gene is needed to see another gene: one recessive allele in one gene will influence a different gene
polygenic inheritance
Broad range of phenotypes
* Trait more complex than present or absent
* True of most genes
Many small differences controlled by multiple genes
Average phenotype is most common
Extremes are uncommon
pedigrees show
family connections
genetic disorders are caused by
allele not functioning properly
cystic fibrosis
mucus clumps in lungs caused by a mutant Cl- ion transport protein
cystic fibrosis is recessive:
fine if you have 1 functioning pump, not fine if 2 mutant alleles make no functional proteins
Huntington’s disease creates
protein clumps that kill brain cells
Huntington’s disease is dominant:
presence of normal allele does not prevent the clumps
genetic screening during pregnancy
-Amniocentesis: remove amniotic fluid and grow fetal cells
-Chorionic villus sampling: remove tissue from fetal portion of placenta
chromosome ___ determines gender
23
female chromosome
XX
male chromosome
XY
sex linked genes:
-gender determining chromosome may lack genes
-One gender has only 1 copy of some genes
*Males in humans
*More likely to display recessive trait
-No matching dominant trait
-Recessive trait can appear in other gender if parent with small chromosome has trait
most x linked disorders are dominant/recessive?
recessive
x linked traits are more common in
males: most genes are missing from Y chromosome
color blindness occurs in many men since
instruction for cone pigments are on X chromosome
x inactivation
Level of trait can be affected by number of instructions
independent assortment
genes are inherited separately IF genes are on different chromosomes
if genes are on the sam chromosome,
alleles tend to inherit together (genes are LINKED)
crossing over
homologous pair swap a section during prophase 1 of meiosis
some chromosome alterations can include
deletion, duplication, inversion, and translocation
deletion:
part of chromosome is lost
oGenes may be removed from lost chromosome
duplication:
selection of chromosome is duplicated
oDuplicated section combined with rest of chromosome
inversion:
piece breaks and is reattached backward
oGenes are in different order than before
translocation
piece of one chromosome is attached to non-homologous chromosome
oNon homologous chromosomes may swap pieces
nonmendelian inheritance: genomic imprinting
: only receive an active copy of gene from one parent
____ and ___ have DNA and genes
mitochondria and chloroplasts
all organelle genes are inherited from
mother
