Recall that to be successful, all things must survive to reproduce

• Reproduction is just one phase of the life cycle but is perhaps the most important.

• Reproduction can be sexual or asexual

Sexual Reproduction

• Incorporation of a sperm AND egg to make an individual

• Gametes: _________ reproductive cells that each contain DNA from _____ ______and combine into offspring

• Tons of variation is possible

Understanding Chromosomes

• A chromosome is a portion of DNA that codes for particular features

• Each feature is located at a particular spot on a particular chromosome (________)

• Human have 23 individual chromosomes that are paired up in a somatic cell– 22 ___________ that

determine everything but sex

– 1 that determines _____

Very varied!• All of our characteristics are held

in 23 pairs of chromosomes• In asexual reproduction all pairs

come from one parent• In sexual reproduction one

chromosome of each pair comes from each parent…

• You have a 50-50 chance of which one you get for each chromosome + combo when put together

+ all 23 times this happens for different characteristics

+ mutation and crossing over = _________________________

– Only identical twins are identical

On to Meiosis… When do we use it

• _________ is a specialized type of cell division that creates _____ __________instead of diploid somatic cells

• Haploid (n) refers to having only _____ _____of chromosomes instead a _______ (2n) cell’s usual ___________ pair.

Meiosis: overview• 2 stages

– Meiosis 1 = ________ _________ ________________

– Meiosis 2 = separate _____ ___________________

• Every cell has a pair of every chromosome– When meiosis begins it has 2

pieces (copies) of each pair…– Pairs separate (blue eyes vs

brown eyes) in meiosis 1– Then in meiosis 2 the copies

separate (two versions of the same thing get pulled apart)

Steps in Meiosis• In prophase I the homologous chromosomes join together (at

the ________ ) and undergo crossing over (swapping identical pieces to increase variation)

• Metaphase I: homologous chromosomes line up• Anaphase I and Telophase I homologous chromosomes

separated• Cytokinesis divides the cells (____ ________ _______

_______________)• Each daughter cell the undergoes prophase II and metaphase

II where the sister chromatids line up• The sister chromatids are separated in anaphase II and

telophase II • Leaving a total of 4 haploid cells with single copies of each

chromosome.

Understanding crossing over

• In Prophase I of meiosis homologous chromosomes undergo a process called crossing over

• This is an exchange of chromosomal segments which insures no two (of 4 total) daughter cells will be exact copies of each other

• New chromosomes that underwent crossing over are called ____________ __________________

Homologous chromosomes

Mitosis vs. Meiosis

Important factors of meiosis1. ___________ _________: the separation of

homologous chromosomes is not dependent on how the other chromosomes separate– For example: Eye color and hair color are not associated, they

are independent. Meaning within a family you will have different combinations of eye and hair color… instead of brown hair = brown eyes

2. Each homologous chromosome caries different versions of the same gene: If you have brown eyes that doesn’t mean that both of your

chromosomes code for brown eyes… one could code for green If you are short you could have a tall gene… so your children can have different features from you and their

other parent but still be yours

When Meiosis goes wrong- Non-disjunction

• When a woman is born all of her eggs (offspring) are already formed and arrested in metaphase II

• When she ovulates the eggs begin to divide again

• Sometimes the chromosomes have been stuck together for too long and won’t easily separate

• Many problems can come from this

Trisomy 21

• Most chromosomes, if duplicated, result in non-viable offspring (they don’t live to birth)

• One notable exception is chromosome ___; it only results in Down Syndrome

• The symptoms include facial features such as a round face, flattened nose, rounded teeth and short stature;

• Things you might not see are heart defects, mental retardation, and increased susceptibility to Alzheimer’s, leukemia and respiratory infection

More on down syndrome• Although 1 out of 700

children in the United States the statistics show that maternal age is a huge factor– Women over in their mid to

late 30s have a 1% chance of having a child with downs, where women under 30 have only a .05% chance

• Parents with downs have a 50% chance of passing it on, with each meiotic event they produce two normal and two abnormal cells

Abnormal #s of sex chromosomes• There are many syndromes that result because there

are many possible combinations• If a father donates two Ys, or a mother or father two

Xs, or if either one donates none the progeny could have a variety of diseases (XYY is a normal male, XXX have limited fertility but appear normal)

Using Karyotypes• A karyotype is ____ _________

_________________________• It can be used to diagnose things

such as down syndrome, and sexual syndromes and is gaining more uses with increased understanding of disease

• Heart disease and even Alzheimer's is being predicted using genetic maps such as this… but there is an ethical question.

• Should we predict what we can’t prevent?

Changes in DNA during replication • Deletion: a portion is removed

– Where is the dog? Where the dog?• Duplication: a portion is doubled

– Where is the dog? Where is the the dog?• Inversion: If a deleted piece reattaches in the wrong

orientation– Where is the dog? Where is dog? Where is dog eht?

• Translocation: removed from chromosome and added randomly to another– Where is the dog? The dog is in the backyard. Where is

dog? The dog is in the backyard the.