Transcript Cells - Troup County High School

Genetics
Georgia High School Graduation Test:
Science Review
Introduction
• From the key vocabulary, circle the
words that you can already define
or use in a sentence.
• Write down two or three things
that you think are important for
you to know today.
Genetics
• The study of the inheritance of
traits and how genes pass on
these traits from parents to
offspring
Important Genetic Vocabulary
• trait: a characteristic of an organism
that is inherited (examples: eye color,
hair type, etc.)
• gene: basic unit of heredity made of
DNA that determines the
characteristics of a trait
• allele: the two different versions of a
gene for a particular trait (one received
from each parent)
Genotype versus
Phenotype
GENOTYPE
• an organism’s genetic
makeup
• includes the two
alleles
• represented with two
letters (example: Bb)
PHENOTYPE
• the physical
appearance of a trait
• expressed by the
organisms genes
• represented by
description (example:
brown eyes)
Dominant versus Recessive
DOMINANT
RECESSIVE
• an allele that expresses
• An allele whose effects
itself while hiding the
are hidden by a dominant
effects of another allele
allele
• represented with a capital • Represented with a
letter
lower-case letter
• example: Bb (dominant
• example: Bb (dominant
brown eyes dominates
brown eyes dominates
over recessive blue)
over recessive blue)
Homozygous versus
Heterozygous
HOMOZYGOUS
• “homo-” means the
same
• the pairing of alleles
that are the same
• examples:
• BB is dominant
homozygous brown
• bb is recessive
homozygous blue
HETEROZYGOUS
• “hetero-” means
different
• the pairing of unlike
alleles
• example:
• Bb is heterozygous
brown
Sample Question
1. Explain how traits are passed
from generation to generation.
Gregor Mendel
• Father of Genetics
• experimented with pea plants
• established a method for
predicting how traits are
inherited
Mendel’s Laws
• The Law of Dominance: a recessive trait will
only be expressed when the organism’s genotype
is recessive homozygous (bb)
• The Law of Segregation: during fertilization,
new alleles are randomly formed; one can only
predict offspring (using Punnett squares)
• The Law of Independent Assortment: each
trait is inherited independently of other traits
Probability and Punnett Squares
• Probability is the likelihood an event will occur
• Geneticists use Punnett squares to predict the
probability of genetic combinations
• Example: When two heterozygous brown eyes
mate . . .
B
b
B
BB
Bb
b
Bb
bb
Theory of Inheritance
• Chromosomes are the physical basis of
inheritance (carry DNA).
• Variability results from dominant and
recessive alleles.
• The chromosomes in the male gamete and
female gamete join together during
fertilization to form a zygote.
• gamete = sex cell
• zygote = fertilized egg
Sample Question
2. Explain the role of DNA and
RNA in heredity.
DNA
• deoxyribonucleic acid
• found in chromosomes in the nucleus
• determines the hereditary traits of an
organism
• contains all the information needed for
the production of proteins
• protein sequences determine traits
RNA
• ribose nucleic acid
• aids in protein synthesis in the ribosome
• 3 types:
• messenger RNA: mRNA carries the DNA
nucleotide sequence for a protein from the
nucleus to the ribosome
• transfer RNA: tRNA transports amino acids
(building blocks of proteins) to the ribosome
• ribosomal RNA: rRNA makes up the
structure of the ribosome
Sample Question
3. Diagram and explain DNA
replication.
DNA replication
• self-duplication of the genetic material
• results in two new DNA molecules
• occurs during interphase (just before cell
divides)
• proteins unwind the DNA helix and each strand
acts as a template for a new strand
• unbound nucleotides attach . . .
• A-T (adenine binds with thymine)
• C-G (cytosine binds with guanine)
Sample Question
4. Diagram and explain
transcription.
DNA transcription
• to “transcribe” is to copy
• mRNA is synthesized in the cell nucleus from
the DNA molecule
• Just as in replication, the helix unwinds and free
nucleotides attach to make mRNA. . .
• C-G (cytosine binds with guanine)
• U-A (uracil binds with adenine)
• Only DNA has thymine
• mRNA separates and moves out of the nucleus
• DNA double helix reforms
Sample Question
5. Diagram and explain
translation.
DNA translation
• process of translating the
genetic code to the amino acid
sequence
• tRNA decodes the mRNA to
read the DNA in order to make
the correct protein
Mutations
• A mutation is any change in the DNA
sequence.
• A change in one nucleotide may cause
a change in the structure of the
protein.
• During pregnancy, observing a
karyotype (a chromosome picture) can
detect chromosomal defects.
Discussion
• If you needed to get precise
information from one person to
another, what would you need to
do? How would you structure the
information? How would you store
that information so that it could be
easily retrieved?
Lesson Summarized
• Write a sentence that explains the
system discussed.
• Draw a graphic organizer that
shows the relationship of the parts
of the gene system to the whole
system.