Ch. 6-9

What are the two types of cell division in eukaryotes?

Meiosis and Mitosis

What types of cells do meiosis create?

Sperm and egg (reproductive) cells ONLY

What happens if there are errors during meiosis?

Nondisjunction (i.e. Down Syndrome)

Define Meiosis

The process that produces haploid gametes in diploid organisms

How many cell divisions occur during meiosis and how many cells are produced?

Twice; four daughter

What is the life cycle?

The cycle as to how a new organism is formed

What is a zygote?

a fertilized egg; a diploid cell

What is an embryo?

the multicellular form that happens to the zygote once mitosis occurs

What is a fetus?

Fetus: after 9 weeks of nine division and once the embryo has formed all of its body parts

Describe the life cycle of a human

1. Each parent has 46 chromosomes
2. Meiosis happens and a haploid cell occurs in both parents
3. The egg is fertilized
4. Mitosis occurs to form the offspring

How are fraternal twins formed? What is another word for fraternal?

The twins come from two completely different zygotes, so they're only 50% identical; dizygotic

How are identical twins formed? What is another word for identical?

The twins come from the same embryo that happened to split, so they're 100% identical; monozygotic

Explain why fathers determine the sex of their offspring, instead of mothers.

The father's sperm could contain an X or a Y, but all eggs have an X.

From whom does a child inherit his/her cytoplasm and organelles?

Almost entirely from the mother

For each cell that undergoes meiosis, what is the final outcome?

Four genetically unique cells

T/F: Crossing over occurs during mitosis

False

A sperm cell that has undergone a nondisjunction will ______

Have too many or too few chromosomes AND Create an offspring with the wrong number of chromosomes in EVERY cell

T/F: Sexually reproducing organisms use meiosis for all their cell division

False

An individual with the unusual sex chromosome combination of XXXY will develop as ________ unless they have a mutation in the SRY gene

a male

How is biological sex determined?

it depends on the type of organism

A straight hairline occurs when a person has two recessive alleles for it. How are these alleles arranged?

These two alleles occur on two different chromosomes that form a homologous pair

In garden peas, an allele R codes for round peas while an allele r codes for wrinkled peas. You cross an rr plant with an Rr plant. What percent of the offspring are wrinkled?

50%

In garden peas, an allele R codes for round peas while an allele r codes for wrinkled peas. You cross an rr plant with an Rr plant. What percent of the offspring are heterozygous?

50%

In garden peas, an allele R codes for round peas while an allele r codes for wrinkled peas. You cross an rr plant with an Rr plant. What genotypes do the offspring have and in what proportions?

1/2 Rr, 1/2 rr

What are 2 reasons why offspring from sexual reproduction are genetically different from their parents & each other?

1) Random fertilization
2) Crossing over

What is random fertilization

Multiple eggs and sperm are produced, each genetically different from one another, and the ones that become zygotes are completely random

What is crossing over?

Exchange of genetic material between homologous chromosomes

Why is crossing over important?

It's the main reason offspring of sexual reproduction are genetically unique

What does crossing over produce?

It produces gene combinations different from those carried by the parents' chromosomes

What causes abnormal chromosome numbers?

Nondisjunction

What is a nondisjunction?

Members of a chromosome pair fail to separate in meiosis

T/F: There is no known cause for nondisjunction.

True

Can nondisjunction lead to abnormal chromosome numbers in autosomes, sex chromosomes, or both?

Both

What happens to a human embryo born with an abnormal # of autosomes?

They'll develop a syndrome

What is a syndrome?

a group of symptoms that result in a condition characterized by a set of associated symptoms.

Do offspring with abnormal numbers of sex chromosomes usually survive?

Yes, they may have down syndrome

What is Down Syndrome?

A condition where individuals are born with an extra chromosome; also called trisomy 21

Do any factors besides sex chromosomes determine gender? If so, describe them.

Yes: The SRY gene- if it has a mutation, one could have a Y chromosome but develop as a girl

What happens to a zygote with the wrong number of autosomes?

Likely results in a miscarriage

. Do both copies of our genes code for the same version of a trait?

No, while one allele carries a trait for blue eyes, the other could be green, but only ONE trait will show

What is an allele?

Each version of a trait

Give an example of an allele and a gene.

• Gene: Hair color/eye color/hair type
• Allele: brown or blue/blue or green/curly or straight

Alleles can be either _________ or ___________

dominant or recessive

What does it mean for an allele to be dominant?

Dominant is a version of a trait that fully shows in the organism; they're represented by capital letters

What does it mean for an allele to be recessive?

Recessive is a version of a trait that can be hidden; they're represented by lowercase letters

What is an example of a homozygous dominant allele? Heterozygous? Homozygous recessive?

RR, Rr, rr

What is a genotype?

An organism's genetic makeup (ex. Aa, BB, or cc)

What is a phenotype?

The trait that an organism is actually showing; What is physically seen on the organism (i.e. blue eyes, red hair)

T/F: Phenotypes are genes passed to the offspring

False (genotypes)

Who discovered the basic patterns of inheritance?

Gregor Mendel

To what kind of human traits do Mendel's principles apply?

Inherited traits from parents that are passed from generation to generation

How are many human disorders determined?

By a single gene on a sex cell (autosome)

Are most disorders dominant or recessive?

Recessive

What are carriers?

Organisms that have 1 recessive allele for disease, but no symptoms

Carriers have a ________________ genotype for the disease

heterozygous

List examples of recessive disorders.

Cystic fibrosis, albinism, sickle cell disease,

Describe cystic fibrosis

A condition where someone makes excess fluids in their lungs to a point where they can suffocate on it unless they can get it out.

What happens when 2 carriers mate?

The child has a 25% chance of getting the disorder

Are dominant alleles necessarily more common than the corresponding recessive allele?

No, just because it's dominant doesn't mean it's better or rarer.

Why are lethal dominant disorders rare?

Because the organisms with the disorder will die before they have children unless they don't show themselves

How can a lethal dominant disorder get passed on from generation to generation?

If the disorder doesn't appear until later in life, like Alzheimer's

List examples of dominant disorders.

Alzheimer's, Huntington's disease

How are human genetic disorders usually studied since we can't do experiments controlling who mates with whom?

By constructing Pedigrees

What are Pedigrees?

A useful tool to document a trait of interest across multiple generations of family members

What is the symbol for a female in a pedigree? A male?

Females are circles, Males are squares

What is the symbol for a marriage or mating?

Marriage is symbolized by a line drawn horizontally between those who are married/matted

How are people with a genetic disorder shown?

Traits of interests that are exhibited are filled in

How can you tell if a trait is recessive or dominant on a pedigree?

If the trait is nonexistent in one generation (a) but present in the next (b), because that means that generation (a) is heterozygous, so generation (b) had the chance of inheriting the recessive trait.

What is a sex-linked gene?

Any gene located on a sex chromosome is called a sex-linked gene

Where are sex-linked genes located?

Always on the X

Do both sex chromosomes have the same number of genes?

NO, X has many more genes than Y

When will a female show a recessive phenotype for a sex-linked trait?

Only if she's homozygous recessive

When will a male show a recessive phenotype for a sex-linked trait

Only if he has one recessive allele

Describe sex-linked disorders.

Some disorders result from recessive alleles on X chromosomes

T/F: Disorders are expressed more by women than men

False

What are two examples of sex-linked disorders?

Hemophilia - disease where blood won't clot correctly
Red-green color blindness

Do Mendel's principles explain all patterns of genetic inheritance?

No

Do genetics influence all characteristics?

No, things like music taste come from you, not your parents

Evolution has 2 meanings to biologists: a __________ and a____________

process; theory

What do biologists mean by the process of evolution?

a change over many generations in the relative frequency of alleles that occur in a population

Why is it important that species are more genetically similar to other species nearby (even in different habitats) than they are to species that live in similar habitats somewhere else?

This pattern indicates that an ancestral population moved into an area and then different individuals of the population began to live in different habitats. These populations in different habitats gradually changed to become slightly different from each other, eventually becoming different species.

T/F: Individuals evolve in response to changing conditions.

False

What is the theory of evolution?

all species are descendants of a single common ancestor, and all species are the result of millions of years of change.

Who was Charles Darwin? What did his book, "Origin of the Species" provide?

The Father of Evolution; his book provided evidence for evolution and his proposed mechanism for doing so (natural selection)

Name three major categories of evidence for evolution

1. Fossils
2. Biogeography
3. Homologies

What are fossils?

the preserved remnants or impressions left by organisms that lived in the past

What are the two ways you can tell the age of fossils?

1. Fossil Record: How far down it occurs
2. Radiometric dating, testing the rock to see how old the particles of it are

What fossils are oldest? How old are they?

Bacteria- 3.5 million years old

What is biogeography?

Biogeography: the study of the geographical distribution of species

Define homology

a similarity in structure due to common ancestry

Where have homologies been found?

• Molecular biology
• Embryology
• Anatomy

How can molecular biology be used to show homologies?

Evolutionary relationships can be studied by comparing the genes and proteins of different organisms

What is comparative embryology

the comparison of structures that appear during the development of different organisms

What is comparative anatomy

the study of similarities and differences in the anatomy of different species. It is closely related to evolutionary biology and phylogeny (the evolution of species).

What are Vestigial structures

leftover structures from a common ancestor that do not have a current purpose

What are the 5 mechanisms that cause a population's allele frequency to change over time

1. Artificial selection
2. Natural selection
3. Genetic drift
4. Gene flow due to migration
5. Mutation

What is artificial selection?

The selective breeding of domesticated plants and animals by humans

What 3 conditions are necessary for natural selection to occur?

1. There has to be variations for a trait
2. There has to be heritability
3. Differential Reproductive Success

Describe what "differential reproductive success" means.

It refers to the difference between individuals in a given generation and how many offspring they are able to leave. The "fittest" leave more offspring while those not suited to the environment leave fewer or even none

Who or what determines which traits are favorable?

The local environment determines what traits are favorable