Genetics Final – Study Guide
Mrs. D’Addario
Section #1: Genetics/Inheritance
vocab:
traits – physical characteristics in organisms that are controlled by genes
genes – Factors that control traits
allele – different forms of a gene/scientist use a letter to represent allele
Hybrid – an organism with two different alleles for a trait (Tt)
homozygous – same alleles for a trait (TT or tt) (AKA = purebred)
heterozygous – different alleles for a trait
(Tt) (AKA = hybrid)
probability – a number that describes how likely it is that an event will occur (in the Punnett
square below there is a 1 in four chance the baby will be purebred for recessive
trait)
Punnett Square – a chart which shows all the possible outcomes (offspring) of genetic crosses
Phenotype – an organism’s physical appearance
genotype – allele combination or genetic makeup
content:
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TT = homozygous dominant (2 dominant alleles for a trait)
Tt = heterozygous alleles for a trait (1 dominant and one recessive allele for a trait)
tt = homozygous recessive alleles for a trait (2 recessive alleles for a trait)
phenotype is determined by genotype. The dominant allele, if present, is ALWAYS seen
(Heterozygous – dominant trait seen)
Gregor Mendel is the father of genetics. He studied Pea Plants and determined that by
cross fertilizing tall and short pea plants the offspring didn’t always resemble parents. In
different generations (F1 and F2) the parent’s phenotypes could return.
Utilize the first letter of the dominant trait to represent alleles! For example if tall plant
is the dominant and a short plant is recessive: T = tall plant / t = short plant
Punnett square review:
T
t (#1 dad’s alleles on top / mom’s on side)
(#2 transfer dad’s alleles down to each box below it)
TT
Tt
T
t
(#3 – transfer all moms’ alleles to boxes on the right
Tt
tt
(#4 – possible offspring in the boxes)
75% tall offspring (25% homozygous dominant & 50% heterozygous)
25% short offspring (25% homozygous recessive)
(#5 – list % of pheno and genotypes of parents and all offspring)
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The environment can interact with genes and cause changes in phenotypes (example:
height in humans can be affected by not eating a balanced diet)
Section #2: Sexual Reproduction
vocab:
gametes – sex cells (aka: germ cells)
fertilization – joining of sex cells (sperm + egg)
zygote – formed when sperm and egg meet (fertilization)
ovulation – a mature egg is released from ovary into the fallopian tube
adolescence – a phase in development when an individual’s body becomes able to reproduce
Content: Meiosis Illustration:
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Meiosis purpose is to make 4 sex cells with ½ the number of chromosomes than a body
cell
Sex cells = Egg (23 chromosome) + Sperm (23 chromosomes)
Egg + sperm = Zygote (46 chromosomes – begin to divide using MITOSIS to make all
body cells)
Egg and sperm meet (fertilize) in the fallopian tube and then travel to the uterus where
it develops into an embryo and then a fetus
female reproductive organs: ovary (eggs produced), fallopian tube (fertilization
happens/passageway for the egg), uterus (fertilized eggs attach and grow here), vagina
(fetus leaves through here after 9 months of development).
menstruation happens when the egg does not become fertilized. The lining of the
uterus becomes thick and leaves the body when the egg does not attach
male reproductive organs: scrotum (pouch of skin surrounds the testes outside of the
body that holds testes away from body), testes (sperm is produced here), tubes (lined
with glands that produce semen), urethra (name of tube that runs the length of the
penis where sperm and urine leave the body), penis (male organ).
human male organisms contain XY alleles on the 23rd chromosome pair
human female organisms contain XX alleles on the 23rd chromosome pair
Section #3: DNA
vocab:
Chromatin - most unorganized genetic material (DNA) in the cell (found in nucleus)
Mutation – a change in a gene or chromosome (addition/deletion or substitution of one or more of the
nitrogen bases)
content:
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DNA found in nucleus of cell
DNA (string of nitrogen bases) to chromatin (strings of genetic material) to chromatid
(matching/identical pairs of organized strings) to chromosome (two chromatids held
together by a centromere)
Chromosomes are made up of genes joined together in a complex form
genetic code is determined by the order or nitrogen bases
a 3 base sequence string forms amino acids which make protein (messenger and
transfer RNA)
DNA bases = A (adenine) and T (thymine)
C (cytosine) and G (guanine)
RNA bases = A and U (uracil takes place of thymine)
C and G
mutations is a change in DNA that can be harmful if it reduces an organism’s chance of
survival and reproduction
Cell Cycle:
o happens in nucleus of the cell
o Has 3 stages:
Interphase (replication of DNA)
Mitosis (distribution of genetic material in two cells)
Cytokinesis (split of cytoplasm)
o Mitosis = 4 phases:
Pro (chromosomes made)
Meta (line up chromosome/attach spindle fibers
Ana (split centromeres and chromatids go to opposite sides of cell
Telo (2 new nuclear envelopes from around chromatids
o Mitosis results in two daughter cells with 46 chromosomes in each
(somatic/body cells)
Section #4: Evolution
Vocab:
evolution – a theory that states species gradually changed over many generations and became
better adapted to new conditions
natural selection – when individuals that are better adapted to their environment are more
likely to survive and reproduce than other members of the same species
species – group of similar organisms that mate with each other and produce fertile offspring
adaptation – a trait that helps an organism survive and reproduce
Content:
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Natural selection has caused the evolution of species
genes control the traits that help organisms to survive (environment naturally selects
them to survive and reproduce)
Section #5: Cell Review
Vocab:
Cell membrane – Controls what leaves and enters the cell
mitochondria – convert energy from food molecules into energy the cell can use
to carry out the cells functions
nucleus – control center of the cell
chloroplast – converts energy from the sun into food for PLANT cells (not in
animal cells)
cell wall – Protect and support PLANT cells (not found in animals)
Content:
lysosome
golgi bodies
endoplasmic reticulum
chromatin
ribosome
nucleolus
nucleus
mitochondria
cell membrane
nuclear envelope